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

ppapi/proxy/ppb_var_proxy.cc

Index: ppapi/proxy/ppb_var_proxy.cc
diff --git a/ppapi/proxy/ppb_var_proxy.cc b/ppapi/proxy/ppb_var_proxy.cc
index 4ee6cc1a347fdea829731bec20b7f78363e2c543..0c7cf5bf75685589eb2b408be8cd77ddd451691a 100644
--- a/ppapi/proxy/ppb_var_proxy.cc
+++ b/ppapi/proxy/ppb_var_proxy.cc
@@ -8,6 +8,7 @@
 #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 {
@@ -18,18 +19,22 @@ 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());