Mention that the widget tree is not disposed on exit (flutter#131637)

Author: Hixie

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

@@ -1152,6 +1152,20 @@ mixin WidgetsBinding on BindingBase, ServicesBinding, SchedulerBinding, GestureB
 ///
 /// Initializes the binding using [WidgetsFlutterBinding] if necessary.
 ///
+/// ## Application shutdown
+///
+/// This widget tree is not torn down when the application shuts down, because
+/// there is no way to predict when that will happen. For example, a user could
+/// physically remove power from their device, or the application could crash
+/// unexpectedly, or the malware on the device could forcibly terminate the
+/// process.
+///
+/// Applications are responsible for ensuring that they are well-behaved
+/// even in the face of a rapid unscheduled termination.
+///
+/// To artificially cause the entire widget tree to be disposed, consider
+/// calling [runApp] with a widget such as [SizedBox.shrink].
+///
 /// See also:
 ///
 ///  * [WidgetsBinding.attachRootWidget], which creates the root widget for the

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

@@ -1238,6 +1238,20 @@ abstract class State<T extends StatefulWidget> with Diagnosticable {
   /// Implementations of this method should end with a call to the inherited
   /// method, as in `super.dispose()`.
   ///
+  /// ## Application shutdown
+  ///
+  /// This method is _not_ invoked when the application shuts down, because
+  /// there is no way to predict when that will happen. For example, a user's
+  /// battery could catch fire, or the user could drop the device into a
+  /// swimming pool, or the operating system could unilaterally terminate the
+  /// application process due to memory pressure.
+  ///
+  /// Applications are responsible for ensuring that they are well-behaved
+  /// even in the face of a rapid unscheduled termination.
+  ///
+  /// To artificially cause the entire widget tree to be disposed, consider
+  /// calling [runApp] with a widget such as [SizedBox.shrink].
+  ///
   /// See also:
   ///
   ///  * [deactivate], which is called prior to [dispose].