Fixes issues when switching between software and compositing.

content/renderer/browser_plugin/browser_plugin_compositing_helper.h

Index: content/renderer/browser_plugin/browser_plugin_compositing_helper.h
diff --git a/content/renderer/browser_plugin/browser_plugin_compositing_helper.h b/content/renderer/browser_plugin/browser_plugin_compositing_helper.h
index 5fd695d617ca6925c5d2ee4d422803141f62845b..9194f2abbef451823e4263278a39d029bf0e326b 100644
--- a/content/renderer/browser_plugin/browser_plugin_compositing_helper.h
+++ b/content/renderer/browser_plugin/browser_plugin_compositing_helper.h
@@ -23,24 +23,33 @@ class WebLayer;
 
 namespace content {
 
-class CONTENT_EXPORT BrowserPluginCompositingHelper {
+class CONTENT_EXPORT BrowserPluginCompositingHelper :
+    public base::RefCounted<BrowserPluginCompositingHelper> {
  public:
   BrowserPluginCompositingHelper(WebKit::WebPluginContainer* container,
                                  int host_routing_id);
-  ~BrowserPluginCompositingHelper();
-
   void EnableCompositing(bool);
+  void OnContainerDestroy();
   void OnBuffersSwapped(const gfx::Size& size,
                         const std::string& mailbox_name,
                         int gpu_route_id,
                         int gpu_host_id);
   void SetContainerSize(const gfx::Size&);
-
+ protected:
+  // Friend RefCounted so that the dtor can be non-public.
+  friend class base::RefCounted<BrowserPluginCompositingHelper>;
  private:
+  ~BrowserPluginCompositingHelper();
+  void FreeMailboxMemory(const std::string& mailbox_name);
+  void MailboxReleased(const std::string& mailbox_name,
+                       int gpu_route_id,
+                       int gpu_host_id,
+                       unsigned sync_point);
   void UpdateUVRect();
 
   int host_routing_id_;
   bool last_mailbox_valid_;
+  bool ack_pending_;
 
   gfx::Size buffer_size_;
   gfx::Size container_size_;