Add explicit base namespace to string16 users.

chrome/common/extensions/api/system_indicator/system_indicator_handler.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 CHROME_COMMON_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_HANDLER_H_
 #define CHROME_COMMON_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_HANDLER_H_
 
 #include "base/strings/string16.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/manifest_handler.h"
 
 namespace extensions {
 
 // Parses the "system_indicator" manifest key.
 class SystemIndicatorHandler : public ManifestHandler {
  public:
   SystemIndicatorHandler();
   virtual ~SystemIndicatorHandler();
 
-  virtual bool Parse(Extension* extension, string16* error) OVERRIDE;
+  virtual bool Parse(Extension* extension, base::string16* error) OVERRIDE;
 
  private:
   virtual const std::vector<std::string> Keys() const OVERRIDE;
 
   DISALLOW_COPY_AND_ASSIGN(SystemIndicatorHandler);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_COMMON_EXTENSIONS_API_SYSTEM_INDICATOR_SYSTEM_INDICATOR_HANDLER_H_