Add PPB_PDF API to load scaled image resources

ppapi/c/private/ppb_pdf.h

 // Copyright (c) 2011 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 PPAPI_C_PRIVATE_PPB_PDF_H_
 #define PPAPI_C_PRIVATE_PPB_PDF_H_
 
 #include "ppapi/c/dev/ppb_font_dev.h"
 #include "ppapi/c/pp_bool.h"
 #include "ppapi/c/pp_instance.h"
@@ skipping 151 matching lines @@
   // Notifies the browser that the PDF has an unsupported feature.
   void (*HasUnsupportedFeature)(PP_Instance instance);
 
   // Invoke SaveAs... dialog, similar to the right-click or wrench menu.
   void (*SaveAs)(PP_Instance instance);
 
   // Invoke Print dialog for plugin.
   void (*Print)(PP_Instance instance);
 
   PP_Bool(*IsFeatureEnabled)(PP_PDFFeature feature);
+
+  // Returns a resource image appropriate for a device with |scale| density.
+  // Returns 0 (NULL resource) if there is no resource at that scale
+  PP_Resource (*GetResourceImageForScale)(PP_Instance instance,
+                                          PP_ResourceImage image_id,
+                                          float scale);
 };
 
 #endif  // PPAPI_C_PRIVATE_PPB_PDF_H_