Introduce webrtc::TaskQueue and TaskQueueFactory interfaces

Bug: webrtc:10191
Change-Id: Ia2fff34cb260d904f25f7263051695f1c004a53b
Reviewed-on: https://webrtc-review.googlesource.com/c/117360
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#26295}
diff --git a/api/task_queue/task_queue_factory.h b/api/task_queue/task_queue_factory.h
new file mode 100644
index 0000000..6827138
--- /dev/null
+++ b/api/task_queue/task_queue_factory.h
@@ -0,0 +1,35 @@
+/*
+ *  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.
+ */
+#ifndef API_TASK_QUEUE_TASK_QUEUE_FACTORY_H_
+#define API_TASK_QUEUE_TASK_QUEUE_FACTORY_H_
+
+#include <memory>
+
+#include "absl/strings/string_view.h"
+#include "api/task_queue/task_queue_base.h"
+#include "api/task_queue/task_queue_priority.h"
+
+namespace webrtc {
+
+class TaskQueueFactory {
+ 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;
+
+  virtual ~TaskQueueFactory() = default;
+  virtual std::unique_ptr<TaskQueueBase, TaskQueueDeleter> CreateTaskQueue(
+      absl::string_view name,
+      Priority priority) const = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // API_TASK_QUEUE_TASK_QUEUE_FACTORY_H_