Tests and empty implementation for FlutterFragment

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

@@ -1689,6 +1689,11 @@ boolean shouldDelayFirstAndroidViewDraw() {
     return getArguments().getBoolean(ARG_SHOULD_DELAY_FIRST_ANDROID_VIEW_DRAW);
   }
 
+  @Override
+  public void setFrameworkHandlesBacks(boolean frameworkHandlesBacks) {
+    // Irrelevant to FlutterFragment.
+  }
+
   private boolean stillAttachedForEvent(String event) {
     if (delegate == null) {
       Log.w(TAG, "FlutterFragment " + hashCode() + " " + event + " called after release.");

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

@@ -92,14 +92,20 @@ public void flutterViewHasId() {
   // test that directly exercises the OnBackInvoked APIs when API 33 is supported.
   @Test
   @TargetApi(33)
-  public void itRegistersOnBackInvokedCallbackOnCreate() {
+  public void itRegistersOnBackInvokedCallbackOnChangingFrameworkHandlesBack() {
     Intent intent = FlutterActivityWithReportFullyDrawn.createDefaultIntent(ctx);
     ActivityController<FlutterActivityWithReportFullyDrawn> activityController =
         Robolectric.buildActivity(FlutterActivityWithReportFullyDrawn.class, intent);
     FlutterActivityWithReportFullyDrawn activity = spy(activityController.get());
 
     activity.onCreate(null);
 
+    verify(activity, times(0)).registerOnBackInvokedCallback();
+
+    activity.setFrameworkHandlesBacks(false);
+    verify(activity, times(0)).registerOnBackInvokedCallback();
+
+    activity.setFrameworkHandlesBacks(true);
     verify(activity, times(1)).registerOnBackInvokedCallback();
   }
 

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

@@ -417,5 +417,8 @@ public void updateSystemUiOverlays() {}
     public boolean popSystemNavigator() {
       return false;
     }
+
+    @Override
+    public void setFrameworkHandlesBacks(boolean frameworkHandlesBacks) {}
   }
 }

shell/platform/android/test/io/flutter/plugin/platform/PlatformPluginTest.java

@@ -469,6 +469,19 @@ public void verifyWindowFlagsSetToStyleOverlays() {
                 | WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION);
   }
 
+  @Test
+  public void setFrameworkHandlesBacksFlutterActivity() {
+    Activity mockActivity = mock(Activity.class);
+    PlatformChannel mockPlatformChannel = mock(PlatformChannel.class);
+    PlatformPluginDelegate mockPlatformPluginDelegate = mock(PlatformPluginDelegate.class);
+    PlatformPlugin platformPlugin =
+        new PlatformPlugin(mockActivity, mockPlatformChannel, mockPlatformPluginDelegate);
+
+    platformPlugin.mPlatformMessageHandler.setFrameworkHandlesBacks(true);
+
+    verify(mockPlatformPluginDelegate, times(1)).setFrameworkHandlesBacks(true);
+  }
+
   @Test
   public void popSystemNavigatorFlutterActivity() {
     Activity mockActivity = mock(Activity.class);