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

content/public/browser/web_drag_dest_delegate.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_BROWSER_WEB_DRAG_DEST_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_DRAG_DEST_DELEGATE_H_
 
 #if defined(TOOLKIT_GTK)
 #include <gtk/gtk.h>
 #endif  // TOOLKIT_GTK
 
-#include "base/string16.h"
+#include "base/strings/string16.h"
 
 #if defined(OS_WIN)
 #include "ui/base/dragdrop/drop_target_win.h"
 #endif
 
 class GURL;
 struct WebDropData;
 
 namespace ui {
 class OSExchangeData;
@@ skipping 44 matching lines @@
   virtual bool AddDragData(const WebDropData& drop_data,
                            ui::OSExchangeData* data) = 0;
 #endif  // TOOLKIT_GTK
 
   virtual ~WebDragDestDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_DRAG_DEST_DELEGATE_H_