Add explicit base namespace to string16 users.

chrome/common/extensions/api/file_browser_handlers/file_browser_handler.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.
 
 #ifndef CHROME_COMMON_EXTENSIONS_API_FILE_BROWSER_HANDLERS_FILE_BROWSER_HANDLER_H_
 #define CHROME_COMMON_EXTENSIONS_API_FILE_BROWSER_HANDLERS_FILE_BROWSER_HANDLER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 74 matching lines @@
   extensions::URLPatternSet url_set_;
 };
 
 // Parses the "file_browser_handlers" extension manifest key.
 class FileBrowserHandlerParser : public extensions::ManifestHandler {
  public:
   FileBrowserHandlerParser();
   virtual ~FileBrowserHandlerParser();
 
   virtual bool Parse(extensions::Extension* extension,
-                     string16* error) OVERRIDE;
+                     base::string16* error) OVERRIDE;
 
  private:
   virtual const std::vector<std::string> Keys() const OVERRIDE;
 };
 
 #endif  // CHROME_COMMON_EXTENSIONS_API_FILE_BROWSER_HANDLERS_FILE_BROWSER_HANDLER_H_