Add support for multimedia timers to TaskQueue on Windows.

webrtc/base/task_queue.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 160 matching lines @@
   // TODO(tommi): For better debuggability, implement RTC_FROM_HERE.
 
   // Ownership of the task is passed to PostTask.
   void PostTask(std::unique_ptr<QueuedTask> task);
   void PostTaskAndReply(std::unique_ptr<QueuedTask> task,
                         std::unique_ptr<QueuedTask> reply,
                         TaskQueue* reply_queue);
   void PostTaskAndReply(std::unique_ptr<QueuedTask> task,
                         std::unique_ptr<QueuedTask> reply);
 
+  // Schedules a task to execute a specified number of milliseconds from when
+  // the call is made. The precision should be considered as "best effort"
+  // and in some cases, such as on Windows when all high precision timers have
+  // been used up, can be off by as much as 15 millseconds (although 8 would be
+  // more likely). This can be mitigated by limiting the use of delayed tasks.
   void PostDelayedTask(std::unique_ptr<QueuedTask> task, uint32_t milliseconds);
 
   template <class Closure>
   void PostTask(const Closure& closure) {
     PostTask(std::unique_ptr<QueuedTask>(new ClosureTask<Closure>(closure)));
   }
 
+  // See documentation above for performance expectations.
   template <class Closure>
   void PostDelayedTask(const Closure& closure, uint32_t milliseconds) {
     PostDelayedTask(
         std::unique_ptr<QueuedTask>(new ClosureTask<Closure>(closure)),
         milliseconds);
   }
 
   template <class Closure1, class Closure2>
   void PostTaskAndReply(const Closure1& task,
                         const Closure2& reply,
@@ skipping 49 matching lines @@
   rtc::CriticalSection pending_lock_;
   std::list<std::unique_ptr<QueuedTask>> pending_ GUARDED_BY(pending_lock_);
   std::list<PostAndReplyTask*> pending_replies_ GUARDED_BY(pending_lock_);
 #elif defined(WEBRTC_MAC)
   struct QueueContext;
   struct TaskContext;
   struct PostTaskAndReplyContext;
   dispatch_queue_t queue_;
   QueueContext* const context_;
 #elif defined(WEBRTC_WIN)
+  class MultimediaTimer;
   typedef std::unordered_map<UINT_PTR, std::unique_ptr<QueuedTask>>
       DelayedTasks;
   static bool ThreadMain(void* context);
-  static bool ProcessQueuedMessages(DelayedTasks* delayed_tasks);
+  static bool ProcessQueuedMessages(DelayedTasks* delayed_tasks,
+                                    std::vector<MultimediaTimer>* timers);
 
   class WorkerThread : public PlatformThread {
    public:
     WorkerThread(ThreadRunFunction func, void* obj, const char* thread_name)
         : PlatformThread(func, obj, thread_name) {}
 
     bool QueueAPC(PAPCFUNC apc_function, ULONG_PTR data) {
       return PlatformThread::QueueAPC(apc_function, data);
     }
   };
   WorkerThread thread_;
 #else
 #error not supported.
 #endif
 
   RTC_DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_TASK_QUEUE_H_