Drop support for link-time injection of the rtc::TaskQueue::Impl

Bug: webrtc:10191
Change-Id: I1b975e8a2230dd45828a4e7f4d5a86f61164445a
Reviewed-on: https://webrtc-review.googlesource.com/c/124121
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26870}
diff --git a/rtc_base/task_queue.h b/rtc_base/task_queue.h
index d6198a8..d5be38b 100644
--- a/rtc_base/task_queue.h
+++ b/rtc_base/task_queue.h
@@ -17,9 +17,9 @@
 #include <utility>
 
 #include "absl/memory/memory.h"
-#include "api/scoped_refptr.h"
 #include "api/task_queue/queued_task.h"
-#include "api/task_queue/task_queue_priority.h"
+#include "api/task_queue/task_queue_base.h"
+#include "api/task_queue/task_queue_factory.h"
 #include "rtc_base/constructor_magic.h"
 #include "rtc_base/system/rtc_export.h"
 #include "rtc_base/thread_annotations.h"
@@ -143,8 +143,7 @@
  public:
   // TaskQueue priority levels. On some platforms these will map to thread
   // priorities, on others such as Mac and iOS, GCD queue priorities.
-  using Priority = ::webrtc::TaskQueuePriority;
-  class Impl;
+  using Priority = ::webrtc::TaskQueueFactory::Priority;
 
   explicit TaskQueue(const char* queue_name,
                      Priority priority = Priority::NORMAL);
@@ -188,15 +187,7 @@
   }
 
  private:
-  // TODO(danilchap): Remove when external implementaions of TaskQueue remove
-  // these two functions.
-  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);
-
-  const scoped_refptr<Impl> impl_;
+  webrtc::TaskQueueBase* const impl_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(TaskQueue);
 };