PDF: Use chrome.resourcesPrivate instead of Pepper to display translated strings

chrome/common/extensions/api/resources_private.idl

 // Copyright 2015 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.
 
 // resourcesPrivate.
 namespace resourcesPrivate {
-  enum Component { identity };
+  enum Component { identity, pdf };
 
   callback GetStringsCallback = void (object result);
 
   interface Functions {
     // Gets localized strings for a component extension. Includes default WebUI
     // loadTimeData values for text and language settings (fontsize, fontfamily,
     // language, textdirection). See
     // chrome/browser/extensions/api/resources_private/resources_private_api.cc
     // for instructions on adding a new component to this API.
     //
     // |component| : Internal chrome component to get strings for.
     // |callback| : Called with a dictionary mapping names to strings.
     static void getStrings(Component component,
                            GetStringsCallback callback);
   };
 };