Remove remaining calls to deprecated MessageLoop methods on Mac.

device/serial/serial_connection_unittest.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 "device/serial/serial_connection.h"
 
 #include <stdint.h>
 
 #include <memory>
 #include <string>
@@ skipping 127 matching lines @@
     stop_run_loop_ = run_loop.QuitClosure();
     run_loop.Run();
   }
 
   void EventReceived(Event event) {
     if (event != expected_event_)
       return;
     expected_event_ = EVENT_NONE;
     ASSERT_TRUE(message_loop_);
     ASSERT_TRUE(!stop_run_loop_.is_null());
-    message_loop_->PostTask(FROM_HERE, stop_run_loop_);
+    message_loop_->task_runner()->PostTask(FROM_HERE, stop_run_loop_);
   }
 
   scoped_refptr<SerialIoHandler> CreateIoHandler() {
     io_handler_ = new TestSerialIoHandler;
     return io_handler_;
   }
 
   void OnDataSent(uint32_t bytes_sent) {
     bytes_sent_ += bytes_sent;
     send_error_ = serial::SendError::NONE;
@@ skipping 173 matching lines @@
   WaitForEvent(EVENT_DATA_SENT);
   EXPECT_EQ(serial::SendError::NONE, send_error_);
   EXPECT_EQ(4, bytes_sent_);
   ASSERT_NO_FATAL_FAILURE(Receive());
   WaitForEvent(EVENT_DATA_RECEIVED);
   EXPECT_EQ("data", data_received_);
   EXPECT_EQ(serial::ReceiveError::NONE, receive_error_);
 }
 
 }  // namespace device