Mac gpu: on gpu<->nongpu transitions, make sure to not show uninitialized memory

chrome/browser/renderer_host/render_widget_host_view_mac.h

 // Copyright (c) 2006-2008 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 CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 #define CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 #pragma once
 
 #import <Cocoa/Cocoa.h>
 #import <QuartzCore/CALayer.h>
@@ skipping 248 matching lines @@
 
   void KillSelf();
 
   void SetTextInputActive(bool active);
 
   // Sends confirmed plugin IME text back to the renderer.
   void PluginImeCompositionConfirmed(const string16& text, int plugin_id);
 
   const std::string& selected_text() const { return selected_text_; }
 
+  void UpdateRootGpuViewVisibility(bool show_gpu_widget);
+
+  // When rendering transitions from gpu to software, the gpu widget can't be
+  // hidden until the software backing store has been updated. This method
+  // checks if the GPU view needs to be hidden and hides it if necessary. It
+  // should be called after the software backing store has been painted to.
+  void HandleDelayedGpuViewHiding();
+
   // These member variables should be private, but the associated ObjC class
   // needs access to them and can't be made a friend.
 
   // The associated Model.  Can be NULL if Destroy() is called when
   // someone (other than superview) has retained |cocoa_view_|.
   RenderWidgetHost* render_widget_host_;
 
   // This is true when we are currently painting and thus should handle extra
   // paint requests by expanding the invalid rect rather than actually painting.
   bool about_to_validate_and_paint_;
@@ skipping 55 matching lines @@
 
   // The text to be shown in the tooltip, supplied by the renderer.
   std::wstring tooltip_text_;
 
   // Factory used to safely scope delayed calls to ShutdownHost().
   ScopedRunnableMethodFactory<RenderWidgetHostViewMac> shutdown_factory_;
 
   // selected text on the renderer.
   std::string selected_text_;
 
+  // When rendering transitions from gpu to software, the gpu widget can't be
+  // hidden until the software backing store has been updated. This variable is
+  // set when the gpu widget needs to be hidden once a paint is completed.
+  bool needs_gpu_visibility_update_after_repaint_;
+
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewMac);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_