Add a unified resource tracker shared between the proxy and the impl.

ppapi/proxy/mock_resource.cc

 // Copyright (c) 2010 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/proxy/mock_resource.h"
 
 using ppapi::HostResource;
+using ppapi::Resource;
 
 namespace pp {
 namespace proxy {
 
-MockResource::MockResource(const HostResource& resource)
-    : PluginResource(resource) {
+MockResource::MockResource(const HostResource& resource) : Resource(resource) {
 }
 
 MockResource::~MockResource() {
 }
 
 }  // namespace proxy
 }  // namespace pp