Add missing IWYU message_loop.h includes.

gpu/command_buffer/client/ring_buffer_test.cc

 // Copyright (c) 2012 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.
 
 // This file contains the tests for the RingBuffer class.
 
 #include "gpu/command_buffer/client/ring_buffer.h"
 
 #include <stdint.h>
 
 #include <memory>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "gpu/command_buffer/client/cmd_buffer_helper.h"
 #include "gpu/command_buffer/service/cmd_buffer_engine.h"
 #include "gpu/command_buffer/service/command_buffer_service.h"
 #include "gpu/command_buffer/service/command_executor.h"
 #include "gpu/command_buffer/service/mocks.h"
 #include "gpu/command_buffer/service/transfer_buffer_manager.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace gpu {
@@ skipping 401 matching lines @@
   // Discarding the middle allocation should turn it into padding.
   allocator_->DiscardBlock(ptr2);
   EXPECT_EQ(0u, allocator_->GetLargestFreeSizeNoWaiting());
 
   // Discarding the first allocation should discard the middle padding as well.
   allocator_->DiscardBlock(ptr1);
   EXPECT_EQ(kAlloc1 + kAlloc2, allocator_->GetLargestFreeSizeNoWaiting());
 }
 
 }  // namespace gpu