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 127 matching lines @@
 
   virtual void RunTest(bool threaded);
 
   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();
 
  private:
   LayerTreeSettings settings_;
   scoped_ptr<LayerTreeHostClientForTesting> client_;
   scoped_ptr<LayerTreeHost> layer_tree_host_;
 
   bool beginning_;
   bool end_when_begin_returns_;
   bool timed_out_;
   bool scheduled_;
@@ skipping 23 matching lines @@
   TEST_F(TEST_FIXTURE_NAME, RunMultiThread) {             \
     RunTest(true);                                        \
   }                                                       \
   class MultiThreadNeedsSemicolon##TEST_FIXTURE_NAME {}
 
 #define SINGLE_AND_MULTI_THREAD_TEST_F(TEST_FIXTURE_NAME) \
   SINGLE_THREAD_TEST_F(TEST_FIXTURE_NAME);                \
   MULTI_THREAD_TEST_F(TEST_FIXTURE_NAME)
 
 #endif  // CC_TEST_LAYER_TREE_TEST_H_