Split out the logic to handle status bar touches into its own function

shell/platform/darwin/ios/framework/Headers/FlutterAppDelegate.h

@@ -29,6 +29,15 @@ FLUTTER_EXPORT
 
 @property(strong, nonatomic) UIWindow* window;
 
+/**
+ * Handle StatusBar touches.
+ *
+ * Call this from your AppDelegate's `touchesBegan:withEvent:` to have Flutter respond to StatusBar
+ * touches.  For example, to enable scroll-to-top behavior.  FlutterAppDelegate already calls it so
+ * you only need to manually call it if you aren't using a FlutterAppDelegate.
+ */
++ (void)handleStatusBarTouches:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event;
+
 @end
 
 #endif  // FLUTTER_FLUTTERDARTPROJECT_H_

shell/platform/darwin/ios/framework/Source/FlutterAppDelegate.mm

@@ -40,21 +40,21 @@ - (BOOL)application:(UIApplication*)application
 
 // Returns the key window's rootViewController, if it's a FlutterViewController.
 // Otherwise, returns nil.
-- (FlutterViewController*)rootFlutterViewController {
++ (FlutterViewController*)rootFlutterViewController {
   UIViewController* viewController = [UIApplication sharedApplication].keyWindow.rootViewController;
   if ([viewController isKindOfClass:[FlutterViewController class]]) {
     return (FlutterViewController*)viewController;
   }
   return nil;
 }
 
-- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event {
-  [super touchesBegan:touches withEvent:event];
++ (void)handleStatusBarTouches:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+  [self.rootFlutterViewController handleStatusBarTouches:event];
+}
 
-  // Pass status bar taps to key window Flutter rootViewController.
-  if (self.rootFlutterViewController != nil) {
-    [self.rootFlutterViewController handleStatusBarTouches:event];
-  }
+- (void)touchesBegan:(NSSet<UITouch*>*)touches withEvent:(UIEvent*)event {
+  [super touchesBegan:touches withEvent:event];
+  [[self class] handleStatusBarTouches:touches withEvent:event];
 }
 
 #pragma GCC diagnostic push