Add support for priorities to TaskQueue.

webrtc/base/task_queue.h

Index: webrtc/base/task_queue.h
diff --git a/webrtc/base/task_queue.h b/webrtc/base/task_queue.h
index 92a1c9477a090cacc7fb4652ccc578a47f3cc359..a1f3def4b2a08de2919c9c997d21da69b584c4ff 100644
--- a/webrtc/base/task_queue.h
+++ b/webrtc/base/task_queue.h
@@ -161,8 +161,15 @@ static std::unique_ptr<QueuedTask> NewClosure(const Closure& closure,
 // so assumptions about lifetimes of pending tasks should not be made.
 class LOCKABLE TaskQueue {
  public:
-  explicit TaskQueue(const char* queue_name);
-  // TODO(tommi): Implement move semantics?

[the sun, 2017/02/24 09:03:43]

Did you mean to remove comment? (FYI: Move semantics on the queue doesn't make a
whole lot of sense to me.)

[tommi, 2017/02/24 17:34:41]

Yeah that's why I removed it. If we find we need it, we can do it but it didn't
feel like this was still worth a todo. besides, the todo had a question mark, so
maybe 'no' is a fine answer and the todo is done :D

+  // TaskQueue priority levels. On some platforms these will map to thread
+  // priorities, on others such as Mac and iOS, GCD queue priorities.
+  enum Priority {

[the sun, 2017/02/24 09:03:43]

We can use enum class these days

[tommi, 2017/02/24 17:34:41]

oooh! completely forgot - Done!

+    NORMAL = 0,
+    HIGH,
+    LOW,
+  };
+
+  explicit TaskQueue(const char* queue_name, Priority priority = NORMAL);
   ~TaskQueue();
 
   static TaskQueue* Current();
@@ -275,8 +282,11 @@ class LOCKABLE TaskQueue {
 
   class WorkerThread : public PlatformThread {
    public:
-    WorkerThread(ThreadRunFunction func, void* obj, const char* thread_name)
-        : PlatformThread(func, obj, thread_name) {}
+    WorkerThread(ThreadRunFunction func,
+                 void* obj,
+                 const char* thread_name,
+                 ThreadPriority priority)
+        : PlatformThread(func, obj, thread_name, priority) {}
 
     bool QueueAPC(PAPCFUNC apc_function, ULONG_PTR data) {
       return PlatformThread::QueueAPC(apc_function, data);