Enable size_t to int truncation warnings in PPAPI

ppapi/cpp/dev/file_chooser_dev.cc

 // Copyright (c) 2012 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.
 
 #include "ppapi/cpp/dev/file_chooser_dev.h"
 
 #include <string.h>
 
 #include "ppapi/c/dev/ppb_file_chooser_dev.h"
 #include "ppapi/c/pp_errors.h"
@@ skipping 64 matching lines @@
     const PPB_FileChooser_Dev_0_5* chooser =
         get_interface<PPB_FileChooser_Dev_0_5>();
     while (PP_Resource cur = chooser->GetNextChosenFile(data->file_chooser))
       selected_files.push_back(cur);
   }
 
   // Need to issue the "GetDataBuffer" even for error cases & when the
   // number of items is 0.
   void* output_buf = data->output.GetDataBuffer(
       data->output.user_data,
-      selected_files.size(), sizeof(PP_Resource));
+      static_cast<uint32_t>(selected_files.size()), sizeof(PP_Resource));
   if (output_buf) {
     if (!selected_files.empty()) {
       memcpy(output_buf, &selected_files[0],
              sizeof(PP_Resource) * selected_files.size());
     }
   } else {
     // Error allocating, need to free the resource IDs.
     for (size_t i = 0; i < selected_files.size(); i++)
       Module::Get()->core()->ReleaseResource(selected_files[i]);
   }
 
   // Now execute the original callback.
   PP_RunCompletionCallback(&data->original_callback, result);
   delete data;
 }
 
 }  // namespace pp