Add explicit base namespace to string16 users.

chrome/common/extensions/manifest_handlers/settings_overrides_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_MANIFEST_HANDLERS_SETTINGS_OVERRIDES_HANDLER_H_
 #define CHROME_COMMON_EXTENSIONS_MANIFEST_HANDLERS_SETTINGS_OVERRIDES_HANDLER_H_
 
 #include "chrome/common/extensions/api/manifest_types.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/manifest_handler.h"
@@ skipping 16 matching lines @@
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SettingsOverrides);
 };
 
 class SettingsOverridesHandler : public ManifestHandler {
  public:
   SettingsOverridesHandler();
   virtual ~SettingsOverridesHandler();
 
-  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(SettingsOverridesHandler);
 };
 
 }  // namespace extensions
 #endif  // CHROME_COMMON_EXTENSIONS_MANIFEST_HANDLERS_SETTINGS_OVERRIDES_HANDLER_H_