Simplify rate limiting since it's main thread shared context only

cc/scheduler/rate_limiter.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_SCHEDULER_RATE_LIMITER_H_
-#define CC_SCHEDULER_RATE_LIMITER_H_
-
-#include "base/memory/ref_counted.h"
-
-namespace base { class SingleThreadTaskRunner; }
-
-namespace WebKit { class WebGraphicsContext3D; }
-
-namespace cc {
-
-class RateLimiterClient {
- public:
-  virtual void RateLimit() = 0;
-
- protected:
-  virtual ~RateLimiterClient() {}
-};
-
-// A RateLimiter can be used to make sure that a single context does not
-// dominate all execution time.  To use, construct a RateLimiter class around
-// the context and call Start() whenever calls are made on the context outside
-// of normal flow control. RateLimiter will block if the context is too far
-// ahead of the compositor.
-class RateLimiter : public base::RefCounted<RateLimiter> {
- public:
-  static scoped_refptr<RateLimiter> Create(
-      WebKit::WebGraphicsContext3D* context,
-      RateLimiterClient* client,
-      base::SingleThreadTaskRunner* task_runner);
-
-  void Start();
-
-  // Context and client will not be accessed after Stop().
-  void Stop();
-
- private:
-  friend class base::RefCounted<RateLimiter>;
-
-  RateLimiter(WebKit::WebGraphicsContext3D* context,
-              RateLimiterClient* client,
-              base::SingleThreadTaskRunner* task_runner);
-  ~RateLimiter();
-
-  void RateLimitContext();
-
-  WebKit::WebGraphicsContext3D* context_;
-  bool active_;
-  RateLimiterClient* client_;
-  base::SingleThreadTaskRunner* task_runner_;
-
-  DISALLOW_COPY_AND_ASSIGN(RateLimiter);
-};
-
-}  // namespace cc
-
-#endif  // CC_SCHEDULER_RATE_LIMITER_H_