[Android] Stop hiding the RWHV layer subtree when hiding the widget

ui/android/window_android_observer.h

Index: ui/android/window_android_observer.h
diff --git a/ui/android/window_android_observer.h b/ui/android/window_android_observer.h
index 05db5ce8f634c894e2d77c79452e7f47bf4b4bfd..4e97d2a51272a63686a3ee96ee7876e3b3ceba14 100644
--- a/ui/android/window_android_observer.h
+++ b/ui/android/window_android_observer.h
@@ -12,12 +12,19 @@ namespace ui {
 class UI_ANDROID_EXPORT WindowAndroidObserver {
  public:
   virtual void OnCompositingDidCommit() = 0;
+  virtual void OnRootWindowVisibilityChanged(bool visible) = 0;
   virtual void OnAttachCompositor() = 0;
   virtual void OnDetachCompositor() = 0;
   virtual void OnVSync(base::TimeTicks frame_time,
                        base::TimeDelta vsync_period) = 0;
   virtual void OnAnimate(base::TimeTicks frame_begin_time) {}
 
+  // Note that activity state callbacks will only be made if the WindowAndroid
+  // has been explicitly subscribed to receive them. The observer instance
+  // should account for whether or not this is the case.
+  virtual void OnActivityPaused() = 0;
+  virtual void OnActivityResumed() = 0;
+
  protected:
   virtual ~WindowAndroidObserver() {}
 };