Capture additional final inset states in ImeSyncDeferringInsetsCallba…

…ck (flutter#42700)

Fixes flutter/flutter#118761.

For some context: ImeSyncDeferringInsetsCallback extends [WindowInsetsAnimation.Callback](https://developer.android.com/reference/android/view/WindowInsetsAnimation.Callback) specifically to handle insets related to keyboard animations.

When a keyboard animation happens, we get a call to onPrepare with the animation, and then to onApplyWindowInsets with [WindowInsets](https://developer.android.com/reference/android/view/WindowInsets) that represent the post animation state. For example, for hiding the keyboard, we would get WindowInsets with height of 0 for insets of type WindowInsets.Type.ime() (input method editor). We save these post-animation insets. 

We then get calls to onProgress for each frame of the animation, and use the WindowInsets passed to onProgress to build new WindowInsets based on the saved post-animation insets, but with the keyboard insets overridden by the WindowInsets passed to onProgress.

Finally, we get a call to onEnd, where we apply the saved insets.

However, there can be multiple animation running at the same time. For example, dismissing the keyboard can result in an animation associated solely with the keyboard happening, as well as an animation associated only with the navigation bar happening. And they can start at slightly different times. This can result in the situation described in this comment: flutter/flutter#118761 (comment)

Re-setting needsSave to false ensures we don't ignore any updates to the final state, ensuring correct insets in onProgress and onEnd.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

shell/platform/android/io/flutter/plugin/editing/ImeSyncDeferringInsetsCallback.java

@@ -119,9 +119,9 @@ private class AnimationCallback extends WindowInsetsAnimation.Callback {
 
     @Override
     public void onPrepare(WindowInsetsAnimation animation) {
+      needsSave = true;
       if ((animation.getTypeMask() & deferredInsetTypes) != 0) {
         animating = true;
-        needsSave = true;
       }
     }
 

shell/platform/android/test/io/flutter/plugin/editing/TextInputPluginTest.java

@@ -2180,6 +2180,87 @@ public void ime_windowInsetsSync_laidOutBehindNavigation_includesNavigationBars(
     assertEquals(100, viewportMetricsCaptor.getValue().viewInsetBottom);
   }
 
+  @Test
+  @TargetApi(30)
+  @Config(sdk = 30)
+  public void lastWindowInsets_updatedOnSecondOnProgressCall() {
+    FlutterView testView = spy(new FlutterView(Robolectric.setupActivity(Activity.class)));
+    when(testView.getWindowSystemUiVisibility()).thenReturn(View.SYSTEM_UI_FLAG_LAYOUT_STABLE);
+
+    TextInputChannel textInputChannel = new TextInputChannel(mock(DartExecutor.class));
+    TextInputPlugin textInputPlugin =
+        new TextInputPlugin(testView, textInputChannel, mock(PlatformViewsController.class));
+    ImeSyncDeferringInsetsCallback imeSyncCallback = textInputPlugin.getImeSyncCallback();
+    FlutterEngine flutterEngine = spy(new FlutterEngine(ctx, mockFlutterLoader, mockFlutterJni));
+    FlutterRenderer flutterRenderer = spy(new FlutterRenderer(mockFlutterJni));
+    when(flutterEngine.getRenderer()).thenReturn(flutterRenderer);
+    testView.attachToFlutterEngine(flutterEngine);
+
+    WindowInsetsAnimation imeAnimation = mock(WindowInsetsAnimation.class);
+    when(imeAnimation.getTypeMask()).thenReturn(WindowInsets.Type.ime());
+    WindowInsetsAnimation navigationBarAnimation = mock(WindowInsetsAnimation.class);
+    when(navigationBarAnimation.getTypeMask()).thenReturn(WindowInsets.Type.navigationBars());
+
+    List<WindowInsetsAnimation> animationList = new ArrayList();
+    animationList.add(imeAnimation);
+    animationList.add(navigationBarAnimation);
+
+    ArgumentCaptor<FlutterRenderer.ViewportMetrics> viewportMetricsCaptor =
+        ArgumentCaptor.forClass(FlutterRenderer.ViewportMetrics.class);
+
+    WindowInsets.Builder builder = new WindowInsets.Builder();
+
+    // Set the initial insets and verify that they were set and the bottom view padding is correct
+    builder.setInsets(WindowInsets.Type.ime(), Insets.of(0, 0, 0, 1000));
+    builder.setInsets(WindowInsets.Type.navigationBars(), Insets.of(0, 0, 0, 100));
+    imeSyncCallback.getInsetsListener().onApplyWindowInsets(testView, builder.build());
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(100, viewportMetricsCaptor.getValue().viewPaddingBottom);
+
+    // Call onPrepare and set the lastWindowInsets - these should be stored for the end of the
+    // animation instead of being applied immediately
+    imeSyncCallback.getAnimationCallback().onPrepare(imeAnimation);
+    builder.setInsets(WindowInsets.Type.ime(), Insets.of(0, 0, 0, 0));
+    builder.setInsets(WindowInsets.Type.navigationBars(), Insets.of(0, 0, 0, 100));
+    imeSyncCallback.getInsetsListener().onApplyWindowInsets(testView, builder.build());
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(100, viewportMetricsCaptor.getValue().viewPaddingBottom);
+
+    // Call onPrepare again and apply new insets - these should overrite lastWindowInsets
+    imeSyncCallback.getAnimationCallback().onPrepare(navigationBarAnimation);
+    builder.setInsets(WindowInsets.Type.ime(), Insets.of(0, 0, 0, 0));
+    builder.setInsets(WindowInsets.Type.navigationBars(), Insets.of(0, 0, 0, 0));
+    imeSyncCallback.getInsetsListener().onApplyWindowInsets(testView, builder.build());
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(100, viewportMetricsCaptor.getValue().viewPaddingBottom);
+
+    // Progress the animation and ensure that the navigation bar insets have not been
+    // subtracted from the IME insets
+    builder.setInsets(WindowInsets.Type.ime(), Insets.of(0, 0, 0, 500));
+    builder.setInsets(WindowInsets.Type.navigationBars(), Insets.of(0, 0, 0, 0));
+    imeSyncCallback.getAnimationCallback().onProgress(builder.build(), animationList);
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().viewPaddingBottom);
+
+    builder.setInsets(WindowInsets.Type.ime(), Insets.of(0, 0, 0, 250));
+    builder.setInsets(WindowInsets.Type.navigationBars(), Insets.of(0, 0, 0, 0));
+    imeSyncCallback.getAnimationCallback().onProgress(builder.build(), animationList);
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().viewPaddingBottom);
+
+    // End the animation and ensure that the bottom insets match the lastWindowInsets that we set
+    // during onPrepare
+    imeSyncCallback.getAnimationCallback().onEnd(imeAnimation);
+
+    verify(flutterRenderer, atLeast(1)).setViewportMetrics(viewportMetricsCaptor.capture());
+    assertEquals(0, viewportMetricsCaptor.getValue().viewPaddingBottom);
+  }
+
   @Test
   @TargetApi(30)
   @Config(sdk = 30)