Add base::test::ScopedTaskEnvironment.

base/test/scoped_task_environment.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_TEST_SCOPED_TASK_ENVIRONMENT_H_
+#define BASE_TEST_SCOPED_TASK_ENVIRONMENT_H_
+
+#include "base/macros.h"
+#include "base/message_loop/message_loop.h"
+
+namespace base {
+
+class TaskScheduler;
+
+namespace test {
+
+// ScopedTaskEnvironment allows usage of these APIs within its scope:
+// - ThreadTaskRunnerHandle, on the thread where it lives

[gab, 2017/04/05 20:44:24]

(Thread|Sequenced)TaskRunnerHandle

[fdoray, 2017/04/06 14:00:23]

Done.

+// - base/task_scheduler/post_task.h, on any thread
+//
+// Tests that need either of these APIs should instantiate a
+// ScopedTaskEnvironment.
+//
+// Tasks posted to the ThreadTaskRunnerHandle run synchronously when
+// RunLoop::Run(UntilIdle) is called on the thread where the
+// ScopedTaskEnvironment lives.
+//
+// Tasks posted through base/task_scheduler/post_task.h run on dedicated threads
+// as they are posted.
+//
+// Future improvements documented in:

[gab, 2017/04/05 20:44:24]

// Design and future improvements documented in

[fdoray, 2017/04/06 14:00:22]

Done.

+// https://docs.google.com/document/d/1QabRo8c7D9LsYY3cEcaPQbOCLo8Tu-6VLykYXyl3Pkk/edit
+class ScopedTaskEnvironment {
+ public:
+  ScopedTaskEnvironment();
+
+  // Runs pending ThreadTaskRunnerHandle tasks and pending BLOCK_SHUTDOWN
+  // TaskScheduler tasks. Then, unregisters the TaskScheduler and the
+  // ThreadTaskRunnerHandle.
+  ~ScopedTaskEnvironment();
+
+ private:
+  MessageLoop message_loop_;

[gab, 2017/04/05 20:44:24]

// Note: |message_loop_| is an implementation detail and will be replaced in the
future, do NOT rely on the presence of a MessageLoop beyond
ThreadTaskRunnerHandle and RunLoop.

[fdoray, 2017/04/06 14:00:23]

Done.

+  const TaskScheduler* task_scheduler_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTaskEnvironment);
+};
+
+}  // namespace test
+}  // namespace base
+
+#endif  // BASE_TEST_SCOPED_ASYNC_TASK_SCHEDULER_H_