Do FinishAllRendering in WM_WINDOWPOSCHANGING

ui/views/win/hwnd_message_handler_delegate.h

 // Copyright (c) 2012 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_VIEWS_WIN_HWND_MESSAGE_HANDLER_DELEGATE_H_
 #define UI_VIEWS_WIN_HWND_MESSAGE_HANDLER_DELEGATE_H_
 
 #include "ui/views/views_export.h"
 
 namespace gfx {
@@ skipping 215 matching lines @@
   // Like PreHandleMSG, but called after HWNDMessageHandler's built-in handling
   // has run and after DefWindowProc.
   virtual void PostHandleMSG(UINT message,
                              WPARAM w_param,
                              LPARAM l_param) = 0;
 
   // Called when a scroll event is received. Returns true if the event was
   // handled by the delegate.
   virtual bool HandleScrollEvent(const ui::ScrollEvent& event) = 0;
 
+  // Called when the window size is about to change.
+  virtual void HandleWindowSizeChanging() = 0;
+
  protected:
   virtual ~HWNDMessageHandlerDelegate() {}
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIN_HWND_MESSAGE_HANDLER_DELEGATE_H_