Reference SizeChangedLayoutNotifier from SizeChangedLayoutNotification (#8887)

Fixes #7520

packages/flutter/lib/src/widgets/size_changed_layout_notifier.dart

@@ -9,12 +9,26 @@ import 'package:flutter/widgets.dart';
 /// this notification has changed, and that therefore any assumptions about that
 /// layout are no longer valid.
 ///
+/// For example, sent by [SizeChangedLayoutNotifier] whenever
+/// [SizeChangedLayoutNotifier] changes size.
+///
+/// This notification for triggering repaints, but if you use this notification
+/// to trigger rebuilds or relayouts, you'll create a backwards dependency in
+/// the frame pipeline because [SizeChangedLayoutNotification]s are generated
+/// during layout, which is after the build phase and in the middle of the
+/// layout phase. This backwards dependency can lead to visual corruption or
+/// lags.
+///
 /// See [LayoutChangedNotification] for additional discussion of layout
 /// notifications such as this one.
+///
+/// See also:
+///
+///  * [SizeChangedLayoutNotifier], which sends this notification.
 class SizeChangedLayoutNotification extends LayoutChangedNotification { }
 
-/// A widget that automatically dispatches a [SizeChangedLayoutNotifier] when
-/// the layout of its child changes.
+/// A widget that automatically dispatches a [SizeChangedLayoutNotification]
+/// when the layout of its child changes.
 ///
 /// Useful especially when having some complex, layout-changing animation within
 /// [Material] that is also interactive.