Add //mojo/edk/platform/thread_utils.* containing "yield" and "sleep".

mojo/edk/platform/thread_utils.h

+// Copyright 2016 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 MOJO_EDK_PLATFORM_THREAD_UTILS_H_
+#define MOJO_EDK_PLATFORM_THREAD_UTILS_H_
+
+#include "mojo/public/c/system/types.h"
+
+namespace mojo {
+namespace platform {
+
+// Causes the calling thread to try to yield (allowing another thread to be
+// scheduled).
+void ThreadYield();
+
+// Causes the calling thread to sleep for at least the specified duration (which
+// must not be |MOJO_DEADLINE_INDEFINITE|).
+void ThreadSleep(MojoDeadline duration);
+
+}  // namespace platform
+}  // namespace mojo
+
+#endif  // MOJO_EDK_PLATFORM_THREAD_UTILS_H_