cc: Remove cc::Thread and cc::ThreadImpl.

cc/base/thread.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_BASE_THREAD_H_
-#define CC_BASE_THREAD_H_
-
-#include "base/basictypes.h"
-#include "base/callback.h"
-#include "base/time.h"
-#include "cc/base/cc_export.h"
-
-namespace base { class SingleThreadTaskRunner; }
-
-namespace cc {
-
-// Thread provides basic infrastructure for messaging with the compositor in a
-// platform-neutral way.
-class CC_EXPORT Thread {
- public:
-  virtual ~Thread() {}
-
-  // Executes the callback on context's thread asynchronously.
-  virtual void PostTask(base::Closure cb) = 0;
-
-  // Executes the task after the specified delay.
-  virtual void PostDelayedTask(base::Closure cb, base::TimeDelta delay) = 0;
-
-  virtual bool BelongsToCurrentThread() const = 0;
-
-  virtual base::SingleThreadTaskRunner* TaskRunner() = 0;
-};
-
-}  // namespace cc
-
-#endif  // CC_BASE_THREAD_H_