[web] Clean up legacy Paragraph implementation

lib/web_ui/lib/src/engine/dom_renderer.dart

@@ -16,7 +16,6 @@ import 'keyboard_binding.dart';
 import 'platform_dispatcher.dart';
 import 'pointer_binding.dart';
 import 'semantics.dart';
-import 'text/measurement.dart';
 import 'text_editing/text_editing.dart';
 import 'util.dart';
 import 'window.dart';
@@ -29,11 +28,6 @@ class DomRenderer {
 
     reset();
 
-    TextMeasurementService.initialize(
-      rulerCacheCapacity: 10,
-      root: _glassPaneShadow!.node,
-    );
-
     assert(() {
       _setupHotRestart();
       return true;

lib/web_ui/lib/src/engine/text/canvas_paragraph.dart

@@ -15,11 +15,13 @@ import 'paint_service.dart';
 import 'paragraph.dart';
 import 'word_breaker.dart';
 
+const ui.Color _defaultTextColor = ui.Color(0xFFFF0000);
+
 /// A paragraph made up of a flat list of text spans and placeholders.
 ///
-/// As opposed to [DomParagraph], a [CanvasParagraph] doesn't use a DOM element
-/// to represent the structure of its spans and styles. Instead it uses a flat
-/// list of [ParagraphSpan] objects.
+/// [CanvasParagraph] doesn't use a DOM element to represent the structure of
+/// its spans and styles. Instead it uses a flat list of [ParagraphSpan]
+/// objects.
 class CanvasParagraph implements EngineParagraph {
   /// This class is created by the engine, and should not be instantiated
   /// or extended directly.
@@ -574,7 +576,7 @@ class RootStyleNode extends StyleNode {
   final EngineParagraphStyle paragraphStyle;
 
   @override
-  final ui.Color _color = defaultTextColor;
+  final ui.Color _color = _defaultTextColor;
 
   @override
   ui.TextDecoration? get _decoration => null;

lib/web_ui/lib/src/engine/text/font_collection.dart

@@ -12,7 +12,6 @@ import '../assets.dart';
 import '../browser_detection.dart';
 import '../util.dart';
 import 'layout_service.dart';
-import 'measurement.dart';
 
 const String ahemFontFamily = 'Ahem';
 const String ahemFontUrl = 'packages/ui/assets/ahem.ttf';
@@ -215,7 +214,6 @@ class FontManager {
       // There might be paragraph measurements for this new font before it is
       // loaded. They were measured using fallback font, so we should clear the
       // cache.
-      TextMeasurementService.clearCache();
       Spanometer.clearRulersCache();
     }, onError: (dynamic exception) {
       // Failures here will throw an html.DomException which confusingly