Move blink scheduler implementation into a component

content/renderer/scheduler/resource_dispatch_throttler.h

 // Copyright 2015 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 CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_
 #define CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_
 
 #include <deque>
 
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/common/content_export.h"
 #include "ipc/ipc_sender.h"
 
+namespace scheduler {
+class RendererScheduler;
+}
+
 namespace content {
 
-class RendererScheduler;
-
 // Utility class for throttling a stream of resource requests targetted to a
 // specific IPC sender. The throttling itself is very basic:
 //  * When there is no high-priority work imminent to the main thread, as
 //    indicated by the RendererScheduler, throttling is disabled.
 //  * When >= N requests have been sent in a given time window, requests are
 //    throttled. A timer periodically flushes a portion of the queued requests
 //    until all such requests have been flushed.
 // TODO(jdduke): Remove this class after resource requests become sufficiently
 // cheap on the IO thread, crbug.com/440037.
 class CONTENT_EXPORT ResourceDispatchThrottler : public IPC::Sender {
  public:
   // |flush_period| and |max_requests_per_flush| must be strictly positive
   // in duration/value.
   ResourceDispatchThrottler(IPC::Sender* proxied_sender,
-                            RendererScheduler* scheduler,
+                            scheduler::RendererScheduler* scheduler,
                             base::TimeDelta flush_period,
                             uint32 max_requests_per_flush);
   ~ResourceDispatchThrottler() override;
 
   // IPC::Sender implementation:
   bool Send(IPC::Message* msg) override;
 
  private:
   friend class ResourceDispatchThrottlerForTest;
 
   // Virtual for testing.
   virtual base::TimeTicks Now() const;
   virtual void ScheduleFlush();
 
   void Flush();
   void FlushAll();
   bool ForwardMessage(IPC::Message* msg);
 
   base::ThreadChecker thread_checker_;
 
   IPC::Sender* const proxied_sender_;
-  RendererScheduler* const scheduler_;
+  scheduler::RendererScheduler* const scheduler_;
   const base::TimeDelta flush_period_;
   const uint32 max_requests_per_flush_;
 
   base::Timer flush_timer_;
   base::TimeTicks last_sent_request_time_;
   uint32 sent_requests_since_last_flush_;
   std::deque<IPC::Message*> throttled_messages_;
 
   DISALLOW_COPY_AND_ASSIGN(ResourceDispatchThrottler);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_SCHEDULER_RESOURCE_DISPATCH_THROTTLER_H_