Connect global task queue factory and rtc::TaskQueue

This cl allows to overwrite TaskQueue implementation
by depending on and setting the global task queue factory.

Bug: webrtc:10191
Change-Id: I69ceb139d00078d3be90eeb4e240758b88829c20
Reviewed-on: https://webrtc-review.googlesource.com/c/118060
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26345}

api/task_queue/task_queue_impl.cc

@@ -0,0 +1,31 @@
+/*
+ *  Copyright 2019 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.
+ */
+#include "api/task_queue/task_queue_impl.h"
+
+#include "rtc_base/checks.h"
+
+namespace rtc {
+
+// Fake ref counting: implementers of the TaskQueueBase shouldn't expect it is
+// stored in a refererence counter pointer.
+void TaskQueue::Impl::AddRef() {
+  // AddRef should be called exactly once by rtc::TaskQueue constructor when
+  // raw pointer converted into scoped_refptr<Impl>,
+  // just before TaskQueue constructor assign task_queue_ member.
+  RTC_CHECK(task_queue_ == nullptr);
+}
+
+void TaskQueue::Impl::Release() {
+  // TaskQueue destructor manually destroyes this object, thus Release should
+  // never be called.
+  RTC_CHECK(false);
+}
+
+}  // namespace rtc