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

chrome/browser/renderer_host/accelerated_surface_container_mac.h

Index: chrome/browser/renderer_host/accelerated_surface_container_mac.h
diff --git a/chrome/browser/renderer_host/accelerated_surface_container_mac.h b/chrome/browser/renderer_host/accelerated_surface_container_mac.h
index de6ceb857fae4fb8f4b7df9d5c3e9d0e395428a9..243692b395589dca30c1740f34bd22ae4f0cb0a9 100644
--- a/chrome/browser/renderer_host/accelerated_surface_container_mac.h
+++ b/chrome/browser/renderer_host/accelerated_surface_container_mac.h
@@ -76,9 +76,12 @@ class AcceleratedSurfaceContainerMac {
   // 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: