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

ppapi/proxy/ppb_var_proxy.cc

 // 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.
 
 #include "ppapi/proxy/ppb_var_proxy.h"
 
 #include "ppapi/c/pp_var.h"
 #include "ppapi/c/ppb_var.h"
 #include "ppapi/proxy/plugin_resource_tracker.h"
 #include "ppapi/proxy/plugin_var_tracker.h"
+#include "ppapi/shared_impl/proxy_lock.h"
 #include "ppapi/shared_impl/var.h"
 
 namespace ppapi {
 namespace proxy {
 
 namespace {
 
 // PPP_Var plugin --------------------------------------------------------------
 
 void AddRefVar(PP_Var var) {
+  ppapi::ProxyAutoLock lock;
   PluginResourceTracker::GetInstance()->var_tracker().AddRefVar(var);
 }
 
 void ReleaseVar(PP_Var var) {
+  ppapi::ProxyAutoLock lock;
   PluginResourceTracker::GetInstance()->var_tracker().ReleaseVar(var);
 }
 
 PP_Var VarFromUtf8(PP_Module module, const char* data, uint32_t len) {
+  ppapi::ProxyAutoLock lock;
   return StringVar::StringToPPVar(module, data, len);
 }
 
 const char* VarToUtf8(PP_Var var, uint32_t* len) {
+  ppapi::ProxyAutoLock lock;
   StringVar* str = StringVar::FromPPVar(var);
   if (str) {
     *len = static_cast<uint32_t>(str->value().size());
     return str->value().c_str();
   }
   *len = 0;
   return NULL;
 }
 
 const PPB_Var var_interface = {
   &AddRefVar,
   &ReleaseVar,
   &VarFromUtf8,
   &VarToUtf8
 };
 
 }  // namespace
 
 const PPB_Var* GetPPB_Var_Interface() {
   return &var_interface;
 }
 
 }  // namespace proxy
 }  // namespace ppapi