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

mojo/edk/system/message_pipe_test_utils.cc

 // Copyright 2014 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.
 
 #include "mojo/edk/system/message_pipe_test_utils.h"
 
 #include <utility>
 
+#include "mojo/edk/platform/thread_utils.h"
 #include "mojo/edk/system/channel.h"
 #include "mojo/edk/system/channel_endpoint.h"
 #include "mojo/edk/system/message_pipe.h"
-#include "mojo/edk/system/test/sleep.h"
 #include "mojo/edk/system/test/timeouts.h"
 #include "mojo/edk/system/waiter.h"
 
 using mojo::platform::ScopedPlatformHandle;
+using mojo::platform::ThreadSleep;
 using mojo::util::MakeRefCounted;
 using mojo::util::RefPtr;
 
 namespace mojo {
 namespace system {
 namespace test {
 
 MojoResult WaitIfNecessary(MessagePipe* mp,
                            MojoHandleSignals signals,
                            HandleSignalsState* signals_state) {
@@ skipping 32 matching lines @@
                               std::move(channel_endpoint));
       });
 }
 
 void ChannelThread::Stop() {
   if (channel_) {
     // Hack to flush write buffers before quitting.
     // TODO(vtl): Remove this once |Channel| has a
     // |FlushWriteBufferAndShutdown()| (or whatever).
     while (!channel_->IsWriteBufferEmpty())
-      test::Sleep(test::EpsilonTimeout());
+      ThreadSleep(test::EpsilonTimeout());
 
     test_io_thread_.PostTaskAndWait([this] {
       channel_->Shutdown();
       channel_ = nullptr;
     });
   }
   test_io_thread_.Stop();
 }
 
 void ChannelThread::InitChannelOnIOThread(
@@ skipping 26 matching lines @@
 }
 
 void MultiprocessMessagePipeTestBase::Init(RefPtr<ChannelEndpoint>&& ep) {
   channel_thread_.Start(helper_.server_platform_handle.Pass(), std::move(ep));
 }
 #endif  // !defined(OS_IOS)
 
 }  // namespace test
 }  // namespace system
 }  // namespace mojo