diff --git a/packages/webview_flutter/lib/platform_interface.dart b/packages/webview_flutter/lib/platform_interface.dart
index df4e3f7d7cca..5d8899ae9e3a 100644
--- a/packages/webview_flutter/lib/platform_interface.dart
+++ b/packages/webview_flutter/lib/platform_interface.dart
@@ -10,11 +10,35 @@ import 'package:flutter/widgets.dart';
 
 import 'webview_flutter.dart';
 
+/// Interface for callbacks made by [WebViewPlatform].
+///
+/// The webview plugin implements this class, and passes an instance to the [WebViewPlatform].
+/// [WebViewPlatform] is notifying this handler on events that happened on the platform's webview.
+abstract class WebViewPlatformCallbacksHandler {
+  /// Invoked by [WebViewPlatform] when a JavaScript channel message is received.
+  void onJavaScriptChannelMessage(String channel, String message);
+
+  /// Invoked by [WebViewPlatform] when a navigation request is pending.
+  ///
+  /// If true is returned the navigation is allowed, otherwise it is blocked.
+  bool onNavigationRequest({String url, bool isForMainFrame});
+
+  /// Invoked by [WebViewPlatform] when a page has finished loading.
+  void onPageFinished(String url);
+}
+
 /// Interface for talking to the webview's platform implementation.
 ///
 /// An instance implementing this interface is passed to the `onWebViewPlatformCreated` callback that is
 /// passed to [WebViewPlatformBuilder#onWebViewPlatformCreated].
 abstract class WebViewPlatform {
+  /// Creates a new WebViewPlatform.
+  ///
+  /// Callbacks made by the WebView will be delegated to `handler`.
+  ///
+  /// The `handler` parameter must not be null.
+  WebViewPlatform(WebViewPlatformCallbacksHandler handler);
+
   /// Loads the specified URL.
   ///
   /// If `headers` is not null and the URL is an HTTP URL, the key value paris in `headers` will
@@ -40,12 +64,94 @@ abstract class WebViewPlatform {
         "WebView updateSettings is not implemented on the current platform");
   }
 
-  // As the PR currently focus about the wiring I've only moved loadUrl to the new way, so
-  // the discussion is more focused.
-  // In this temporary state WebViewController still uses a method channel directly for all other
-  // method calls so we need to expose the webview ID.
-  // TODO(amirh): remove this before publishing this package.
-  int get id;
+  /// Accessor to the current URL that the WebView is displaying.
+  ///
+  /// If no URL was ever loaded, returns `null`.
+  Future<String> currentUrl() {
+    throw UnimplementedError(
+        "WebView currentUrl is not implemented on the current platform");
+  }
+
+  /// Checks whether there's a back history item.
+  Future<bool> canGoBack() {
+    throw UnimplementedError(
+        "WebView canGoBack is not implemented on the current platform");
+  }
+
+  /// Checks whether there's a forward history item.
+  Future<bool> canGoForward() {
+    throw UnimplementedError(
+        "WebView canGoForward is not implemented on the current platform");
+  }
+
+  /// Goes back in the history of this WebView.
+  ///
+  /// If there is no back history item this is a no-op.
+  Future<void> goBack() {
+    throw UnimplementedError(
+        "WebView goBack is not implemented on the current platform");
+  }
+
+  /// Goes forward in the history of this WebView.
+  ///
+  /// If there is no forward history item this is a no-op.
+  Future<void> goForward() {
+    throw UnimplementedError(
+        "WebView goForward is not implemented on the current platform");
+  }
+
+  /// Reloads the current URL.
+  Future<void> reload() {
+    throw UnimplementedError(
+        "WebView reload is not implemented on the current platform");
+  }
+
+  /// Clears all caches used by the [WebView].
+  ///
+  /// The following caches are cleared:
+  ///	1. Browser HTTP Cache.
+  ///	2. [Cache API](https://developers.google.com/web/fundamentals/instant-and-offline/web-storage/cache-api) caches.
+  ///    These are not yet supported in iOS WkWebView. Service workers tend to use this cache.
+  ///	3. Application cache.
+  ///	4. Local Storage.
+  Future<void> clearCache() {
+    throw UnimplementedError(
+        "WebView clearCache is not implemented on the current platform");
+  }
+
+  /// Evaluates a JavaScript expression in the context of the current page.
+  ///
+  /// The Future completes with an error if a JavaScript error occurred, or if the type of the
+  /// evaluated expression is not supported(e.g on iOS not all non primitive type can be evaluated).
+  Future<String> evaluateJavascript(String javascriptString) {
+    throw UnimplementedError(
+        "WebView evaluateJavascript is not implemented on the current platform");
+  }
+
+  /// Adds new JavaScript channels to the set of enabled channels.
+  ///
+  /// For each value in this list the platform's webview should make sure that a corresponding
+  /// property with a postMessage method is set on `window`. For example for a JavaScript channel
+  /// named `Foo` it should be possible for JavaScript code executing in the webview to do
+  ///
+  /// ```javascript
+  /// Foo.postMessage('hello');
+  /// ```
+  ///
+  /// See also: [CreationParams.javascriptChannelNames].
+  Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) {
+    throw UnimplementedError(
+        "WebView addJavascriptChannels is not implemented on the current platform");
+  }
+
+  /// Removes JavaScript channel names from the set of enabled channels.
+  ///
+  /// This disables channels that were previously enabled by [addJavaScriptChannels] or through
+  /// [CreationParams.javascriptChannelNames].
+  Future<void> removeJavascriptChannels(Set<String> javascriptChannelNames) {
+    throw UnimplementedError(
+        "WebView removeJavascriptChannels is not implemented on the current platform");
+  }
 }
 
 /// Settings for configuring a WebViewPlatform.
@@ -125,6 +231,9 @@ abstract class WebViewBuilder {
   ///
   /// `creationParams` are the initial parameters used to setup the webview.
   ///
+  /// `webViewPlatformHandler` will be used for handling callbacks that are made by the created
+  /// [WebViewPlatform].
+  ///
   /// `onWebViewPlatformCreated` will be invoked after the platform specific [WebViewPlatform]
   /// implementation is created with the [WebViewPlatform] instance as a parameter.
   ///
@@ -135,12 +244,15 @@ abstract class WebViewBuilder {
   /// recognizers on this list.
   /// When `gestureRecognizers` is empty or null, the web view will only handle pointer events for gestures that
   /// were not claimed by any other gesture recognizer.
+  ///
+  /// `webViewPlatformHandler` must not be null.
   Widget build({
     BuildContext context,
     // TODO(amirh): convert this to be the actual parameters.
     // I'm starting without it as the PR is starting to become pretty big.
     // I'll followup with the conversion PR.
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   });
diff --git a/packages/webview_flutter/lib/src/webview_android.dart b/packages/webview_flutter/lib/src/webview_android.dart
index 7304e9bce22c..8d5f98a61512 100644
--- a/packages/webview_flutter/lib/src/webview_android.dart
+++ b/packages/webview_flutter/lib/src/webview_android.dart
@@ -20,9 +20,11 @@ class AndroidWebViewBuilder implements WebViewBuilder {
   Widget build({
     BuildContext context,
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   }) {
+    assert(webViewPlatformCallbacksHandler != null);
     return GestureDetector(
       // We prevent text selection by intercepting the long press event.
       // This is a temporary stop gap due to issues with text selection on Android:
@@ -39,7 +41,8 @@ class AndroidWebViewBuilder implements WebViewBuilder {
           if (onWebViewPlatformCreated == null) {
             return;
           }
-          onWebViewPlatformCreated(MethodChannelWebViewPlatform(id));
+          onWebViewPlatformCreated(MethodChannelWebViewPlatform(
+              id, webViewPlatformCallbacksHandler));
         },
         gestureRecognizers: gestureRecognizers,
         // WebView content is not affected by the Android view's layout direction,
diff --git a/packages/webview_flutter/lib/src/webview_cupertino.dart b/packages/webview_flutter/lib/src/webview_cupertino.dart
index aba0a8d264d5..04ca9d78eabc 100644
--- a/packages/webview_flutter/lib/src/webview_cupertino.dart
+++ b/packages/webview_flutter/lib/src/webview_cupertino.dart
@@ -20,6 +20,7 @@ class CupertinoWebViewBuilder implements WebViewBuilder {
   Widget build({
     BuildContext context,
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   }) {
@@ -29,7 +30,8 @@ class CupertinoWebViewBuilder implements WebViewBuilder {
         if (onWebViewPlatformCreated == null) {
           return;
         }
-        onWebViewPlatformCreated(MethodChannelWebViewPlatform(id));
+        onWebViewPlatformCreated(
+            MethodChannelWebViewPlatform(id, webViewPlatformCallbacksHandler));
       },
       gestureRecognizers: gestureRecognizers,
       creationParams:
diff --git a/packages/webview_flutter/lib/src/webview_method_channel.dart b/packages/webview_flutter/lib/src/webview_method_channel.dart
index 4166f9078399..d86a8b4cd2e7 100644
--- a/packages/webview_flutter/lib/src/webview_method_channel.dart
+++ b/packages/webview_flutter/lib/src/webview_method_channel.dart
@@ -10,13 +10,36 @@ import '../platform_interface.dart';
 
 /// A [WebViewPlatform] that uses a method channel to control the webview.
 class MethodChannelWebViewPlatform implements WebViewPlatform {
-  MethodChannelWebViewPlatform(this._id)
-      : _channel = MethodChannel('plugins.flutter.io/webview_$_id');
+  MethodChannelWebViewPlatform(int id, this._platformCallbacksHandler)
+      : assert(_platformCallbacksHandler != null),
+        _channel = MethodChannel('plugins.flutter.io/webview_$id') {
+    _channel.setMethodCallHandler(_onMethodCall);
+  }
 
-  final int _id;
+  final WebViewPlatformCallbacksHandler _platformCallbacksHandler;
 
   final MethodChannel _channel;
 
+  Future<bool> _onMethodCall(MethodCall call) async {
+    switch (call.method) {
+      case 'javascriptChannelMessage':
+        final String channel = call.arguments['channel'];
+        final String message = call.arguments['message'];
+        _platformCallbacksHandler.onJavaScriptChannelMessage(channel, message);
+        return true;
+      case 'navigationRequest':
+        return _platformCallbacksHandler.onNavigationRequest(
+          url: call.arguments['url'],
+          isForMainFrame: call.arguments['isForMainFrame'],
+        );
+      case 'onPageFinished':
+        _platformCallbacksHandler.onPageFinished(call.arguments['url']);
+        return null;
+    }
+    throw MissingPluginException(
+        '${call.method} was invoked but has no handler');
+  }
+
   @override
   Future<void> loadUrl(
     String url,
@@ -32,6 +55,27 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
     });
   }
 
+  @override
+  Future<String> currentUrl() => _channel.invokeMethod('currentUrl');
+
+  @override
+  Future<bool> canGoBack() => _channel.invokeMethod("canGoBack");
+
+  @override
+  Future<bool> canGoForward() => _channel.invokeMethod("canGoForward");
+
+  @override
+  Future<void> goBack() => _channel.invokeMethod("goBack");
+
+  @override
+  Future<void> goForward() => _channel.invokeMethod("goForward");
+
+  @override
+  Future<void> reload() => _channel.invokeMethod("reload");
+
+  @override
+  Future<void> clearCache() => _channel.invokeMethod("clearCache");
+
   @override
   Future<void> updateSettings(WebSettings settings) {
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
@@ -44,6 +88,23 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
     return _channel.invokeMethod('updateSettings', updatesMap);
   }
 
+  @override
+  Future<String> evaluateJavascript(String javascriptString) {
+    return _channel.invokeMethod('evaluateJavascript', javascriptString);
+  }
+
+  @override
+  Future<void> addJavascriptChannels(Set<String> javascriptChannelNames) {
+    return _channel.invokeMethod(
+        'addJavascriptChannels', javascriptChannelNames.toList());
+  }
+
+  @override
+  Future<void> removeJavascriptChannels(Set<String> javascriptChannelNames) {
+    return _channel.invokeMethod(
+        'removeJavascriptChannels', javascriptChannelNames.toList());
+  }
+
   static Map<String, dynamic> _webSettingsToMap(WebSettings settings) {
     final Map<String, dynamic> map = <String, dynamic>{};
     void _addIfNonNull(String key, dynamic value) {
@@ -71,7 +132,4 @@ class MethodChannelWebViewPlatform implements WebViewPlatform {
       'javascriptChannelNames': creationParams.javascriptChannelNames.toList(),
     };
   }
-
-  @override
-  int get id => _id;
 }
diff --git a/packages/webview_flutter/lib/webview_flutter.dart b/packages/webview_flutter/lib/webview_flutter.dart
index a6126d709531..dd7e9203a667 100644
--- a/packages/webview_flutter/lib/webview_flutter.dart
+++ b/packages/webview_flutter/lib/webview_flutter.dart
@@ -264,11 +264,14 @@ class _WebViewState extends State<WebView> {
   final Completer<WebViewController> _controller =
       Completer<WebViewController>();
 
+  _PlatformCallbacksHandler _platformCallbacksHandler;
+
   @override
   Widget build(BuildContext context) {
     return WebView.platformBuilder.build(
       context: context,
       onWebViewPlatformCreated: _onWebViewPlatformCreated,
+      webViewPlatformCallbacksHandler: _platformCallbacksHandler,
       gestureRecognizers: widget.gestureRecognizers,
       creationParams: _creationParamsfromWidget(widget),
     );
@@ -278,19 +281,22 @@ class _WebViewState extends State<WebView> {
   void initState() {
     super.initState();
     _assertJavascriptChannelNamesAreUnique();
+    _platformCallbacksHandler = _PlatformCallbacksHandler(widget);
   }
 
   @override
   void didUpdateWidget(WebView oldWidget) {
     super.didUpdateWidget(oldWidget);
     _assertJavascriptChannelNamesAreUnique();
-    _controller.future.then(
-        (WebViewController controller) => controller._updateWidget(widget));
+    _controller.future.then((WebViewController controller) {
+      _platformCallbacksHandler._widget = widget;
+      controller._updateWidget(widget);
+    });
   }
 
-  void _onWebViewPlatformCreated(WebViewPlatform platformController) {
+  void _onWebViewPlatformCreated(WebViewPlatform webViewPlatform) {
     final WebViewController controller =
-        WebViewController._(platformController.id, platformController, widget);
+        WebViewController._(widget, webViewPlatform, _platformCallbacksHandler);
     _controller.complete(controller);
     if (widget.onWebViewCreated != null) {
       widget.onWebViewCreated(controller);
@@ -360,63 +366,70 @@ Set<String> _extractChannelNames(Set<JavascriptChannel> channels) {
   return channelNames;
 }
 
+class _PlatformCallbacksHandler implements WebViewPlatformCallbacksHandler {
+  _PlatformCallbacksHandler(this._widget) {
+    _updateJavascriptChannelsFromSet(_widget.javascriptChannels);
+  }
+
+  WebView _widget;
+
+  // Maps a channel name to a channel.
+  final Map<String, JavascriptChannel> _javascriptChannels =
+      <String, JavascriptChannel>{};
+
+  @override
+  void onJavaScriptChannelMessage(String channel, String message) {
+    _javascriptChannels[channel].onMessageReceived(JavascriptMessage(message));
+  }
+
+  @override
+  bool onNavigationRequest({String url, bool isForMainFrame}) {
+    final NavigationRequest request =
+        NavigationRequest._(url: url, isForMainFrame: isForMainFrame);
+    final bool allowNavigation = _widget.navigationDelegate == null ||
+        _widget.navigationDelegate(request) == NavigationDecision.navigate;
+    return allowNavigation;
+  }
+
+  @override
+  void onPageFinished(String url) {
+    if (_widget.onPageFinished != null) {
+      _widget.onPageFinished(url);
+    }
+  }
+
+  void _updateJavascriptChannelsFromSet(Set<JavascriptChannel> channels) {
+    _javascriptChannels.clear();
+    if (channels == null) {
+      return;
+    }
+    for (JavascriptChannel channel in channels) {
+      _javascriptChannels[channel.name] = channel;
+    }
+  }
+}
+
 /// Controls a [WebView].
 ///
 /// A [WebViewController] instance can be obtained by setting the [WebView.onWebViewCreated]
 /// callback for a [WebView] widget.
 class WebViewController {
   WebViewController._(
-    int id,
-    this._platformInterface,
     this._widget,
-  ) : _channel = MethodChannel('plugins.flutter.io/webview_$id') {
+    this._webViewPlatform,
+    this._platformCallbacksHandler,
+  ) : assert(_webViewPlatform != null) {
     _settings = _webSettingsFromWidget(_widget);
-    _updateJavascriptChannelsFromSet(_widget.javascriptChannels);
-    _channel.setMethodCallHandler(_onMethodCall);
   }
 
-  final MethodChannel _channel;
+  final WebViewPlatform _webViewPlatform;
 
-  final WebViewPlatform _platformInterface;
+  final _PlatformCallbacksHandler _platformCallbacksHandler;
 
   WebSettings _settings;
 
   WebView _widget;
 
-  // Maps a channel name to a channel.
-  Map<String, JavascriptChannel> _javascriptChannels =
-      <String, JavascriptChannel>{};
-
-  Future<bool> _onMethodCall(MethodCall call) async {
-    switch (call.method) {
-      case 'javascriptChannelMessage':
-        final String channel = call.arguments['channel'];
-        final String message = call.arguments['message'];
-        _javascriptChannels[channel]
-            .onMessageReceived(JavascriptMessage(message));
-        return true;
-      case 'navigationRequest':
-        final NavigationRequest request = NavigationRequest._(
-          url: call.arguments['url'],
-          isForMainFrame: call.arguments['isForMainFrame'],
-        );
-        // _navigationDelegate can be null if the widget was rebuilt with no
-        // navigation delegate after a navigation happened and just before we
-        // got the navigationRequest message.
-        final bool allowNavigation = _widget.navigationDelegate == null ||
-            _widget.navigationDelegate(request) == NavigationDecision.navigate;
-        return allowNavigation;
-      case 'onPageFinished':
-        if (_widget.onPageFinished != null) {
-          _widget.onPageFinished(call.arguments['url']);
-        }
-
-        return null;
-    }
-    throw MissingPluginException(
-        '${call.method} was invoked but has no handler');
-  }
-
   /// Loads the specified URL.
   ///
   /// If `headers` is not null and the URL is an HTTP URL, the key value paris in `headers` will
@@ -431,7 +444,7 @@ class WebViewController {
   }) async {
     assert(url != null);
     _validateUrlString(url);
-    return _platformInterface.loadUrl(url, headers);
+    return _webViewPlatform.loadUrl(url, headers);
   }
 
   /// Accessor to the current URL that the WebView is displaying.
@@ -441,64 +454,43 @@ class WebViewController {
   /// current URL changes again by the time this function returns (in other
   /// words, by the time this future completes, the WebView may be displaying a
   /// different URL).
-  Future<String> currentUrl() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    final String url = await _channel.invokeMethod('currentUrl');
-    return url;
+  Future<String> currentUrl() {
+    return _webViewPlatform.currentUrl();
   }
 
   /// Checks whether there's a back history item.
   ///
   /// Note that this operation is asynchronous, and it is possible that the "canGoBack" state has
   /// changed by the time the future completed.
-  Future<bool> canGoBack() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    final bool canGoBack = await _channel.invokeMethod("canGoBack");
-    return canGoBack;
+  Future<bool> canGoBack() {
+    return _webViewPlatform.canGoBack();
   }
 
   /// Checks whether there's a forward history item.
   ///
   /// Note that this operation is asynchronous, and it is possible that the "canGoForward" state has
   /// changed by the time the future completed.
-  Future<bool> canGoForward() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    final bool canGoForward = await _channel.invokeMethod("canGoForward");
-    return canGoForward;
+  Future<bool> canGoForward() {
+    return _webViewPlatform.canGoForward();
   }
 
   /// Goes back in the history of this WebView.
   ///
   /// If there is no back history item this is a no-op.
-  Future<void> goBack() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    return _channel.invokeMethod("goBack");
+  Future<void> goBack() {
+    return _webViewPlatform.goBack();
   }
 
   /// Goes forward in the history of this WebView.
   ///
   /// If there is no forward history item this is a no-op.
-  Future<void> goForward() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    return _channel.invokeMethod("goForward");
+  Future<void> goForward() {
+    return _webViewPlatform.goForward();
   }
 
   /// Reloads the current URL.
-  Future<void> reload() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    return _channel.invokeMethod("reload");
+  Future<void> reload() {
+    return _webViewPlatform.reload();
   }
 
   /// Clears all caches used by the [WebView].
@@ -512,10 +504,7 @@ class WebViewController {
   ///
   /// Note: Calling this method also triggers a reload.
   Future<void> clearCache() async {
-    // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
-    // https://github.com/flutter/flutter/issues/26431
-    // ignore: strong_mode_implicit_dynamic_method
-    await _channel.invokeMethod("clearCache");
+    await _webViewPlatform.clearCache();
     return reload();
   }
 
@@ -529,41 +518,25 @@ class WebViewController {
     final WebSettings update =
         _clearUnchangedWebSettings(_settings, newSettings);
     _settings = newSettings;
-    return _platformInterface.updateSettings(update);
+    return _webViewPlatform.updateSettings(update);
   }
 
   Future<void> _updateJavascriptChannels(
       Set<JavascriptChannel> newChannels) async {
-    final Set<String> currentChannels = _javascriptChannels.keys.toSet();
+    final Set<String> currentChannels =
+        _platformCallbacksHandler._javascriptChannels.keys.toSet();
     final Set<String> newChannelNames = _extractChannelNames(newChannels);
     final Set<String> channelsToAdd =
         newChannelNames.difference(currentChannels);
     final Set<String> channelsToRemove =
         currentChannels.difference(newChannelNames);
     if (channelsToRemove.isNotEmpty) {
-      // TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
-      // https://github.com/flutter/flutter/issues/26431
-      // ignore: strong_mode_implicit_dynamic_method
-      _channel.invokeMethod(
-          'removeJavascriptChannels', channelsToRemove.toList());
+      _webViewPlatform.removeJavascriptChannels(channelsToRemove);
     }
     if (channelsToAdd.isNotEmpty) {
-      // TODO(amirh): remove this when the invokeMethod update makes it to stable Flutter.
-      // https://github.com/flutter/flutter/issues/26431
-      // ignore: strong_mode_implicit_dynamic_method
-      _channel.invokeMethod('addJavascriptChannels', channelsToAdd.toList());
-    }
-    _updateJavascriptChannelsFromSet(newChannels);
-  }
-
-  void _updateJavascriptChannelsFromSet(Set<JavascriptChannel> channels) {
-    _javascriptChannels.clear();
-    if (channels == null) {
-      return;
-    }
-    for (JavascriptChannel channel in channels) {
-      _javascriptChannels[channel.name] = channel;
+      _webViewPlatform.addJavascriptChannels(channelsToAdd);
     }
+    _platformCallbacksHandler._updateJavascriptChannelsFromSet(newChannels);
   }
 
   /// Evaluates a JavaScript expression in the context of the current page.
@@ -582,20 +555,19 @@ class WebViewController {
   /// When evaluating Javascript in a [WebView], it is best practice to wait for
   /// the [WebView.onPageFinished] callback. This guarantees all the Javascript
   /// embedded in the main frame HTML has been loaded.
-  Future<String> evaluateJavascript(String javascriptString) async {
+  Future<String> evaluateJavascript(String javascriptString) {
     if (_settings.javascriptMode == JavascriptMode.disabled) {
-      throw FlutterError(
-          'JavaScript mode must be enabled/unrestricted when calling evaluateJavascript.');
+      return Future<String>.error(FlutterError(
+          'JavaScript mode must be enabled/unrestricted when calling evaluateJavascript.'));
     }
     if (javascriptString == null) {
-      throw ArgumentError('The argument javascriptString must not be null. ');
+      return Future<String>.error(
+          ArgumentError('The argument javascriptString must not be null.'));
     }
     // TODO(amirh): remove this on when the invokeMethod update makes it to stable Flutter.
     // https://github.com/flutter/flutter/issues/26431
     // ignore: strong_mode_implicit_dynamic_method
-    final String result =
-        await _channel.invokeMethod('evaluateJavascript', javascriptString);
-    return result;
+    return _webViewPlatform.evaluateJavascript(javascriptString);
   }
 }
 
diff --git a/packages/webview_flutter/test/webview_flutter_test.dart b/packages/webview_flutter/test/webview_flutter_test.dart
index 7176756bb79b..2a458ad434b7 100644
--- a/packages/webview_flutter/test/webview_flutter_test.dart
+++ b/packages/webview_flutter/test/webview_flutter_test.dart
@@ -1025,7 +1025,7 @@ class _FakeCookieManager {
         });
         break;
     }
-    return Future<bool>.sync(() {});
+    return Future<bool>.sync(() => null);
   }
 
   void reset() {
@@ -1040,18 +1040,22 @@ class MyWebViewBuilder implements WebViewBuilder {
   Widget build({
     BuildContext context,
     CreationParams creationParams,
+    @required WebViewPlatformCallbacksHandler webViewPlatformCallbacksHandler,
     @required WebViewPlatformCreatedCallback onWebViewPlatformCreated,
     Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers,
   }) {
     assert(onWebViewPlatformCreated != null);
-    lastPlatformBuilt = MyWebViewPlatform(creationParams, gestureRecognizers);
+    lastPlatformBuilt = MyWebViewPlatform(
+        creationParams, gestureRecognizers, webViewPlatformCallbacksHandler);
     onWebViewPlatformCreated(lastPlatformBuilt);
     return Container();
   }
 }
 
 class MyWebViewPlatform extends WebViewPlatform {
-  MyWebViewPlatform(this.creationParams, this.gestureRecognizers);
+  MyWebViewPlatform(this.creationParams, this.gestureRecognizers,
+      WebViewPlatformCallbacksHandler platformHandler)
+      : super(platformHandler);
 
   CreationParams creationParams;
   Set<Factory<OneSequenceGestureRecognizer>> gestureRecognizers;
@@ -1066,10 +1070,6 @@ class MyWebViewPlatform extends WebViewPlatform {
     lastRequestHeaders = headers;
     return null;
   }
-
-  @override
-  // TODO: implement id
-  int get id => 1;
 }
 
 class MatchesWebSettings extends Matcher {