cc: Cleanup class/struct forward declarations

cc/trees/single_thread_proxy.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_SINGLE_THREAD_PROXY_H_
 #define CC_TREES_SINGLE_THREAD_PROXY_H_
 
 #include <limits>
 
 #include "base/cancelable_callback.h"
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/scheduler/scheduler.h"
 #include "cc/trees/blocking_task_runner.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/proxy.h"
 #include "cc/trees/task_runner_provider.h"
 
 namespace cc {
 
 class MutatorEvents;
 class BeginFrameSource;
-class ContextProvider;
 class LayerTreeHostInProcess;
 class LayerTreeHostSingleThreadClient;
 
 class CC_EXPORT SingleThreadProxy : public Proxy,
                                     NON_EXPORTED_BASE(LayerTreeHostImplClient),
                                     public SchedulerClient {
  public:
   static std::unique_ptr<Proxy> Create(
       LayerTreeHostInProcess* layer_tree_host,
       LayerTreeHostSingleThreadClient* client,
@@ skipping 198 matching lines @@
  private:
   DebugScopedSetImplThread impl_thread_;
   DebugScopedSetMainThreadBlocked main_thread_blocked_;
 
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetImplThreadAndMainThreadBlocked);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_SINGLE_THREAD_PROXY_H_