Shouldn't access LayerTreeTest::layer_tree_host on impl thread

cc/test/layer_tree_test.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_TEST_LAYER_TREE_TEST_H_
 #define CC_TEST_LAYER_TREE_TEST_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/threading/thread.h"
 #include "cc/base/thread.h"
@@ skipping 128 matching lines @@
                        bool delegating_renderer,
                        bool impl_side_painting);
 
   Thread* ImplThread() { return proxy() ? proxy()->ImplThread() : NULL; }
   Proxy* proxy() const {
     return layer_tree_host_ ? layer_tree_host_->proxy() : NULL;
   }
 
   bool TestEnded() const { return ended_; }
 
-  LayerTreeHost* layer_tree_host() { return layer_tree_host_.get(); }
+  LayerTreeHost* layer_tree_host();
   bool delegating_renderer() const { return delegating_renderer_; }
 
   virtual scoped_ptr<OutputSurface> CreateOutputSurface() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForMainThread() OVERRIDE;
   virtual scoped_refptr<cc::ContextProvider>
       OffscreenContextProviderForCompositorThread() OVERRIDE;
 
  private:
   LayerTreeSettings settings_;
@@ skipping 68 matching lines @@
 
 #define SINGLE_AND_MULTI_THREAD_DELEGATING_RENDERER_TEST_F(TEST_FIXTURE_NAME) \
   SINGLE_THREAD_DELEGATING_RENDERER_TEST_F(TEST_FIXTURE_NAME);                \
   MULTI_THREAD_DELEGATING_RENDERER_TEST_F(TEST_FIXTURE_NAME)
 
 #define SINGLE_AND_MULTI_THREAD_TEST_F(TEST_FIXTURE_NAME) \
   SINGLE_AND_MULTI_THREAD_DIRECT_RENDERER_TEST_F(TEST_FIXTURE_NAME);    \
   SINGLE_AND_MULTI_THREAD_DELEGATING_RENDERER_TEST_F(TEST_FIXTURE_NAME)
 
 #endif  // CC_TEST_LAYER_TREE_TEST_H_