Add missing IWYU message_loop.h includes.

content/browser/storage_partition_impl_map_unittest.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.
 
 #include "content/browser/storage_partition_impl_map.h"
 
 #include <utility>
 
 #include "base/files/file_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/test/test_browser_context.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace content {
 
 // Test that the Less comparison function is implemented properly to uniquely
 // identify storage partitions used as keys in a std::map.
 TEST(StoragePartitionConfigTest, OperatorLess) {
@@ skipping 67 matching lines @@
   storage_partition_impl_map.GarbageCollect(std::move(active_paths),
                                             run_loop.QuitClosure());
   run_loop.Run();
   BrowserThread::GetBlockingPool()->FlushForTesting();
 
   EXPECT_TRUE(base::PathExists(active_path));
   EXPECT_FALSE(base::PathExists(inactive_path));
 }
 
 }  // namespace content