Add missing IWYU message_loop.h includes.

content/browser/shareable_file_reference_unittest.cc

 // Copyright 2015 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 "storage/browser/blob/shareable_file_reference.h"
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using storage::ShareableFileReference;
 
 namespace content {
 
 TEST(ShareableFileReferenceTest, TestReferences) {
@@ skipping 34 matching lines @@
   // Drop the second reference, the file and reference should get deleted.
   reference2 = NULL;
   EXPECT_FALSE(ShareableFileReference::Get(file).get());
   base::RunLoop().RunUntilIdle();
   EXPECT_FALSE(base::PathExists(file));
 
   // TODO(michaeln): add a test for files that aren't deletable behavior.
 }
 
 }  // namespace content