Make tree id sequence in LayerTreeHost thread-safe.

cc/trees/layer_tree_host.h

 // Copyright 2011 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 CC_TREES_LAYER_TREE_HOST_H_
 #define CC_TREES_LAYER_TREE_HOST_H_
 
 #include <limits>
 #include <list>
 #include <string>
@@ skipping 103 matching lines @@
   // The SharedBitmapManager will be used on the compositor thread.
   static scoped_ptr<LayerTreeHost> Create(
       LayerTreeHostClient* client,
       SharedBitmapManager* manager,
       const LayerTreeSettings& settings,
       scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner);
   virtual ~LayerTreeHost();
 
   void SetLayerTreeHostClientReady();
 
-  // Returns true if any LayerTreeHost is alive.
-  static bool AnyLayerTreeHostInstanceExists();
-
   void set_needs_filter_context() { needs_filter_context_ = true; }
   bool needs_offscreen_context() const {
     return needs_filter_context_;
   }
 
   // LayerTreeHost interface to Proxy.
   void WillBeginMainFrame() { client_->WillBeginMainFrame(); }
   void DidBeginMainFrame();
   void UpdateClientAnimations(base::TimeTicks monotonic_frame_begin_time);
   void AnimateLayers(base::TimeTicks monotonic_frame_begin_time);
@@ skipping 321 matching lines @@
   scoped_refptr<Layer> outer_viewport_scroll_layer_;
 
   SharedBitmapManager* shared_bitmap_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_H_