Use a direct include of strings headers in content/p*/.

content/public/test/mock_render_thread.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_TEST_MOCK_RENDER_THREAD_H_
 #define CONTENT_PUBLIC_TEST_MOCK_RENDER_THREAD_H_
 
 #include "base/shared_memory.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "content/public/renderer/render_thread.h"
 #include "ipc/ipc_test_sink.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebPopupType.h"
 
 struct ViewHostMsg_CreateWindow_Params;
 
 namespace IPC {
 class MessageReplyDeserializer;
 }
 
@@ skipping 132 matching lines @@
   // The last known good deserializer for sync messages.
   scoped_ptr<IPC::MessageReplyDeserializer> reply_deserializer_;
 
   // A list of message filters added to this thread.
   std::vector<scoped_refptr<IPC::ChannelProxy::MessageFilter> > filters_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_TEST_MOCK_RENDER_THREAD_H_