Add TimeController to api/test/ and add a CreateTimeController API.

Creates an abstraction for an "alarm clock" which can schedule
time-controller callbacks and exposes a time controller driven by
an external alarm.

Bug: webrtc:9719
Change-Id: I08c2aa9dba25603043bfba48f55c925716a55bae
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158969
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Bjorn Mellem <mellem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29879}
diff --git a/api/test/create_time_controller.cc b/api/test/create_time_controller.cc
new file mode 100644
index 0000000..1d6f24e
--- /dev/null
+++ b/api/test/create_time_controller.cc
@@ -0,0 +1,24 @@
+/*
+ *  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/test/create_time_controller.h"
+
+#include <memory>
+
+#include "test/time_controller/external_time_controller.h"
+
+namespace webrtc {
+
+std::unique_ptr<TimeController> CreateTimeController(
+    ControlledAlarmClock* alarm) {
+  return std::make_unique<ExternalTimeController>(alarm);
+}
+
+}  // namespace webrtc