[webview_flutter_android] Updates the Dart InstanceManager to take a listener for when an object is garbage collected (#6148)

Author: bparrishMines

packages/webview_flutter/webview_flutter_android/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 2.9.3
+
+* Updates the Dart InstanceManager to take a listener for when an object is garbage collected.
+  See https://github.com/flutter/flutter/issues/107199.
+
 ## 2.9.2
 
 * Updates the Java InstanceManager to take a listener for when an object is garbage collected.

packages/webview_flutter/webview_flutter_android/lib/src/android_webview.dart

@@ -28,6 +28,11 @@ abstract class JavaObject with Copyable {
   /// This should only be used by subclasses created by this library or to
   /// create copies.
   JavaObject.detached();
+
+  /// Global instance of [InstanceManager].
+  static final InstanceManager globalInstanceManager = InstanceManager(
+    onWeakReferenceRemoved: (_) {},
+  );
 }
 
 /// An Android View that displays web pages.