Android: Remove WindowAndroidObserver::OnWillDestroyWindow()

ui/base/android/window_android_observer.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_ANDROID_WINDOW_ANDROID_OBSERVER_H_
 #define UI_BASE_ANDROID_WINDOW_ANDROID_OBSERVER_H_
 
 #include "ui/base/ui_base_export.h"
 
 namespace ui {
 
 class UI_BASE_EXPORT WindowAndroidObserver {
  public:
   virtual void OnCompositingDidCommit() = 0;
   virtual void OnAttachCompositor() = 0;
   virtual void OnDetachCompositor() = 0;
-  virtual void OnWillDestroyWindow() = 0;
   virtual void OnVSync(base::TimeTicks frame_time,
                        base::TimeDelta vsync_period) = 0;
   virtual void OnAnimate(base::TimeTicks frame_begin_time) {}
 
  protected:
   virtual ~WindowAndroidObserver() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_ANDROID_WINDOW_ANDROID_OBSERVER_H_