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

chrome/browser/renderer_host/accelerated_surface_container_mac.h

 // Copyright (c) 2010 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_GPU_PLUGIN_CONTAINER_MAC_H_
 #define CHROME_BROWSER_RENDERER_HOST_GPU_PLUGIN_CONTAINER_MAC_H_
 #pragma once
 
 // The "GPU plugin" is currently implemented as a special kind of
 // NPAPI plugin to provide high-performance on-screen 3D rendering for
@@ skipping 58 matching lines @@
 
   // Draws this accelerated surface's contents, texture mapped onto a quad in
   // the given OpenGL context. TODO(kbr): figure out and define exactly how the
   // coordinate system will work out.
   void Draw(CGLContextObj context);
 
   // Causes the next Draw call to trigger a texture upload. Should be called any
   // time the drawing context has changed.
   void ForceTextureReload() { texture_needs_upload_ = true; }
 
-  // Notifies the surface that it was painted to.
+  // Notifies the the container that its surface was painted to.
   void set_was_painted_to(uint64 surface_id);
 
+  // Notifies the container that its surface is invalid.
+  void set_surface_invalid() { was_painted_to_ = false; }
+
   // Returns if the surface should be shown.
   bool should_be_visible() const { return visible_ && was_painted_to_; }
  private:
   // The manager of this accelerated surface container.
   AcceleratedSurfaceContainerManagerMac* manager_;
 
   // Whether this accelerated surface's content is supposed to be opaque.
   bool opaque_;
 
   // The IOSurfaceRef, if any, that has been handed from the GPU
@@ skipping 42 matching lines @@
   void ReleaseIOSurface();
 
   // Enqueue our texture for later deletion.
   void EnqueueTextureForDeletion();
 
   DISALLOW_COPY_AND_ASSIGN(AcceleratedSurfaceContainerMac);
 };
 
 #endif  // CHROME_BROWSER_RENDERER_HOST_GPU_PLUGIN_CONTAINER_MAC_H_