Move more message handlers from NativeWidgetWin to HWNDMessageHandler.

ui/views/widget/hwnd_message_handler.h

Index: ui/views/widget/hwnd_message_handler.h
===================================================================
--- ui/views/widget/hwnd_message_handler.h	(revision 152375)
+++ ui/views/widget/hwnd_message_handler.h	(working copy)
@@ -65,6 +65,7 @@
   void OnSetFocus(HWND last_focused_window);
   LRESULT OnSetIcon(UINT size_type, HICON new_icon);
   LRESULT OnSetText(const wchar_t* text);
+  void OnSize(UINT param, const CSize& size);
   void OnThemeChanged();
   void OnVScroll(int scroll_type, short position, HWND scrollbar);
 
@@ -74,6 +75,11 @@
     remove_standard_frame_ = remove_standard_frame;
   }
 
+  // Resets the window region for the current widget bounds if necessary.
+  // If |force| is true, the window region is reset to NULL even for native
+  // frame windows.
+  void ResetWindowRegion(bool force);
+
  private:
   // TODO(beng): This won't be a style violation once this object becomes the
   //             WindowImpl.