Test using a global, replacable TaskQueueImpl factory.

webrtc/rtc_base/task_queue_impl.h

+/*
+ *  Copyright 2017 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.
+ */
+
+#ifndef WEBRTC_RTC_BASE_TASK_QUEUE_IMPL_H_
+#define WEBRTC_RTC_BASE_TASK_QUEUE_IMPL_H_
+
+#include <memory>
+
+#include "webrtc/rtc_base/refcount.h"
+#include "webrtc/rtc_base/scoped_ref_ptr.h"
+#include "webrtc/rtc_base/task_queue.h"
+
+namespace rtc {
+
+class TaskQueueImpl : public RefCountInterface {
+ public:
+  virtual bool IsCurrent() const = 0;
+  virtual void PostTask(std::unique_ptr<QueuedTask> task) = 0;
+  virtual void PostTaskAndReply(std::unique_ptr<QueuedTask> task,
+                                std::unique_ptr<QueuedTask> reply,
+                                TaskQueueImpl* reply_queue) = 0;
+  virtual void PostDelayedTask(std::unique_ptr<QueuedTask> task,
+                               uint32_t milliseconds) = 0;
+};
+
+}  // namespace rtc
+#endif  // WEBRTC_RTC_BASE_TASK_QUEUE_IMPL_H_