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

content/public/browser/download_item.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.
 //
 // Each download is represented by a DownloadItem, and all DownloadItems
 // are owned by the DownloadManager which maintains a global list of all
 // downloads. DownloadItems are created when a user initiates a download,
 // and exist for the duration of the browser life time.
 //
 // Download observers:
 //   DownloadItem::Observer:
 //     - allows observers to receive notifications about one download from start
 //       to completion
 // Use AddObserver() / RemoveObserver() on the appropriate download object to
 // receive state updates.
 
 #ifndef CONTENT_PUBLIC_BROWSER_DOWNLOAD_ITEM_H_
 #define CONTENT_PUBLIC_BROWSER_DOWNLOAD_ITEM_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/callback_forward.h"
 #include "base/files/file_path.h"
-#include "base/string16.h"
+#include "base/strings/string16.h"
 #include "base/supports_user_data.h"
 #include "content/public/browser/download_danger_type.h"
 #include "content/public/browser/download_interrupt_reasons.h"
 #include "content/public/common/page_transition_types.h"
 
 class GURL;
 
 namespace base {
 class FilePath;
 class Time;
@@ skipping 292 matching lines @@
   // return |name|. Has no effect on the final target filename.
   virtual void SetDisplayName(const base::FilePath& name) = 0;
 
   // Debug/testing -------------------------------------------------------------
   virtual std::string DebugString(bool verbose) const = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_DOWNLOAD_ITEM_H_