cc: Make sure we don't insert or remove layers during painting

cc/trees/layer_tree_host.h

Index: cc/trees/layer_tree_host.h
diff --git a/cc/trees/layer_tree_host.h b/cc/trees/layer_tree_host.h
index 4f38352f9c69f2129e4d9ebe9c39c47fc4272753..d7d3fb933379a04d7342bc7b342f94b48d487344 100644
--- a/cc/trees/layer_tree_host.h
+++ b/cc/trees/layer_tree_host.h
@@ -87,6 +87,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
     ~InitParams();
   };
 
+  bool in_update() const { return in_update_; }
+
   // The SharedBitmapManager will be used on the compositor thread.
   static scoped_ptr<LayerTreeHost> CreateThreaded(
       scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner,
@@ -478,6 +480,8 @@ class CC_EXPORT LayerTreeHost : public MutatorHostClient {
   gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager_;
   TaskGraphRunner* task_graph_runner_;
 
+  bool in_update_;
+
   ScopedPtrVector<SwapPromise> swap_promise_list_;
   std::set<SwapPromiseMonitor*> swap_promise_monitor_;