Use a direct include of strings headers in webkit/, part 1.

webkit/common/webdropdata.h

 // Copyright 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.
 //
 // A struct for managing data being dropped on a webview.  This represents a
 // union of all the types of data that can be dropped in a platform neutral
 // way.
 
 #ifndef WEBKIT_COMMON_WEBDROPDATA_H_
 #define WEBKIT_COMMON_WEBDROPDATA_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/nullable_string16.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "googleurl/src/gurl.h"
 #include "third_party/WebKit/public/platform/WebReferrerPolicy.h"
 #include "webkit/common/webkit_common_export.h"
 
 struct IDataObject;
 
 namespace WebKit {
 class WebDragData;
 }
 
@@ skipping 43 matching lines @@
   GURL html_base_url;
 
   // User is dragging data from the webview (e.g., an image).
   base::string16 file_description_filename;
   std::string file_contents;
 
   std::map<base::string16, base::string16> custom_data;
 };
 
 #endif  // WEBKIT_COMMON_WEBDROPDATA_H_