cc: Clean up LayerTreeTest and TestHooks.

cc/test/threaded_channel_for_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_THREADED_CHANNEL_FOR_TEST_H_
 #define CC_TEST_THREADED_CHANNEL_FOR_TEST_H_
 
-#include "base/macros.h"
-#include "cc/test/test_hooks.h"
 #include "cc/trees/threaded_channel.h"
 
 namespace cc {
-class ProxyImplForTest;
 
-// ThreadedChannel that notifies |test_hooks| of internal actions by ProxyImpl.
 class ThreadedChannelForTest : public ThreadedChannel {
  public:
-  static std::unique_ptr<ThreadedChannelForTest> Create(
-      TestHooks* test_hooks,
-      ProxyMain* proxy_main,
-      TaskRunnerProvider* task_runner_provider);
-
-  ProxyImplForTest* proxy_impl_for_test() { return proxy_impl_for_test_; }
-
- private:
-  ThreadedChannelForTest(TestHooks* test_hooks,
-                         ProxyMain* proxy_main,
+  ThreadedChannelForTest(ProxyMain* proxy_main,
                          TaskRunnerProvider* task_runner_provider);
 
+  ProxyImpl* proxy_impl() { return proxy_impl_; }
+
+ protected:
+  // ThreadedChannel overrides.
   std::unique_ptr<ProxyImpl> CreateProxyImpl(
       ChannelImpl* channel_impl,
       LayerTreeHost* layer_tree_host,
       TaskRunnerProvider* task_runner_provider,
       std::unique_ptr<BeginFrameSource> external_begin_frame_source) override;
 
-  TestHooks* test_hooks_;
-  ProxyImplForTest* proxy_impl_for_test_;
+ private:
+  ProxyImpl* proxy_impl_ = nullptr;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_THREADED_CHANNEL_FOR_TEST_H_