Bug 695845 - Part 3: Add Flush() and Disconnect() methods to ImageContainer. r=cjones

gfx/layers/ImageLayers.h

@@ -184,6 +184,20 @@ public:
    */
   virtual already_AddRefed<Image> GetCurrentImage() = 0;
 
+  /**
+   * Make sure the current image is ready for rendering by this container.
+   * May only be called from the main thread.
+   */
+  virtual void Flush() {}
+
+  /**
+   * |Disconnect()| is used by ImageContainer hooked up over IPC.  It may 
+   * be called at any time, and may not be called at all.  Using an
+   * IPC-enabled layer after Destroy() (drawing etc.) results in a
+   * safe no-op; no crashy or uaf etc.
+   */
+  virtual void Disconnect() {}
+
   /**
    * Get the current image as a gfxASurface. This is useful for fallback
    * rendering.