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

content/public/browser/web_ui_data_source.h

 // Copyright (c) 2013 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_BROWSER_WEB_UI_DATA_SOURCE_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_UI_DATA_SOURCE_H_
 
-#include "base/string16.h"
 #include "base/callback.h"
+#include "base/strings/string16.h"
 #include "content/common/content_export.h"
 
 namespace base {
 class DictionaryValue;
 class RefCountedMemory;
 }
 
 namespace content {
 class BrowserContext;
 
@@ skipping 62 matching lines @@
   virtual void OverrideContentSecurityPolicyObjectSrc(
       const std::string& data) = 0;
   virtual void OverrideContentSecurityPolicyFrameSrc(
       const std::string& data) = 0;
   virtual void DisableDenyXFrameOptions() = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_UI_DATA_SOURCE_H_