Make much of the proxy thread-safe with 1 great big lock.

ppapi/proxy/plugin_resource_tracker.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_PROXY_PLUGIN_RESOURCE_TRACKER_H_
 #define PPAPI_PROXY_PLUGIN_RESOURCE_TRACKER_H_
 
 #include <map>
 #include <utility>
 
 #include "base/compiler_specific.h"
+#include "base/synchronization/lock.h"
 #include "ppapi/c/pp_completion_callback.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_var.h"
 #include "ppapi/proxy/plugin_var_tracker.h"
 #include "ppapi/proxy/ppapi_proxy_export.h"
 #include "ppapi/shared_impl/host_resource.h"
 #include "ppapi/shared_impl/resource_tracker.h"
 #include "ppapi/shared_impl/tracker_base.h"
@@ skipping 62 matching lines @@
   PluginVarTracker var_tracker_;
 
   // Non-owning pointer to a var tracker mock used by tests. NULL when no
   // test implementation is provided.
   PluginVarTracker* var_tracker_test_override_;
 
   // Map of host instance/resource pairs to a plugin resource ID.
   typedef std::map<HostResource, PP_Resource> HostResourceMap;
   HostResourceMap host_resource_map_;
 
+  // The global lock for the plugin side of the proxy.
+  base::Lock proxy_lock_;
+
   DISALLOW_COPY_AND_ASSIGN(PluginResourceTracker);
 };
 
 }  // namespace proxy
 }  // namespace ppapi
 
 #endif  // PPAPI_PROXY_PLUGIN_RESOURCE_TRACKER_H_