Give FlutterView a view ID (flutter#27052)

shell/platform/android/io/flutter/embedding/android/FlutterActivity.java

@@ -209,6 +209,14 @@ public class FlutterActivity extends Activity
     implements FlutterActivityAndFragmentDelegate.Host, LifecycleOwner {
   private static final String TAG = "FlutterActivity";
 
+  /**
+   * The ID of the {@code FlutterView} created by this activity.
+   *
+   * <p>This ID can be used to lookup {@code FlutterView} in the Android view hierarchy. For more,
+   * see {@link android.view.View#findViewById}.
+   */
+  public static final int FLUTTER_VIEW_ID = 0xF1F2;
+
   /**
    * Creates an {@link Intent} that launches a {@code FlutterActivity}, which creates a {@link
    * FlutterEngine} that executes a {@code main()} Dart entrypoint, and displays the "/" route as
@@ -424,7 +432,11 @@ protected void onCreate(@Nullable Bundle savedInstanceState) {
     lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
 
     configureWindowForTransparency();
-    setContentView(createFlutterView());
+
+    View flutterView = createFlutterView();
+    flutterView.setId(FLUTTER_VIEW_ID);
+    setContentView(flutterView);
+
     configureStatusBarForFullscreenFlutterExperience();
   }
 

shell/platform/android/test/io/flutter/embedding/android/FlutterActivityTest.java

@@ -68,6 +68,17 @@ public void tearDown() {
     FlutterInjector.reset();
   }
 
+  @Test
+  public void flutterViewHasId() {
+    Intent intent = FlutterActivity.createDefaultIntent(RuntimeEnvironment.application);
+    ActivityController<FlutterActivity> activityController =
+        Robolectric.buildActivity(FlutterActivity.class, intent);
+    FlutterActivity activity = activityController.get();
+
+    activity.onCreate(null);
+    assertNotNull(activity.findViewById(FlutterActivity.FLUTTER_VIEW_ID));
+  }
+
   @Test
   public void itCreatesDefaultIntentWithExpectedDefaults() {
     Intent intent = FlutterActivity.createDefaultIntent(RuntimeEnvironment.application);