PPAPI: Add locking for PPB_MessageLoop

ppapi/proxy/ppb_message_loop_proxy.cc

Index: ppapi/proxy/ppb_message_loop_proxy.cc
diff --git a/ppapi/proxy/ppb_message_loop_proxy.cc b/ppapi/proxy/ppb_message_loop_proxy.cc
index c0e9ae174da68d63a333206b30a9e62698c864c6..0062fb7a84f937fa365eae675da6f431f5789d73 100644
--- a/ppapi/proxy/ppb_message_loop_proxy.cc
+++ b/ppapi/proxy/ppb_message_loop_proxy.cc
@@ -198,6 +198,7 @@ void MessageLoopResource::ReleaseMessageLoop(void* value) {
 // -----------------------------------------------------------------------------
 
 PP_Resource Create(PP_Instance instance) {
+  ProxyAutoLock lock;
   // Validate the instance.
   PluginDispatcher* dispatcher = PluginDispatcher::GetForInstance(instance);
   if (!dispatcher)
@@ -206,10 +207,12 @@ PP_Resource Create(PP_Instance instance) {
 }
 
 PP_Resource GetForMainThread() {
+  ProxyAutoLock lock;
   return PluginGlobals::Get()->loop_for_main_thread()->GetReference();
 }
 
 PP_Resource GetCurrent() {
+  ProxyAutoLock lock;
   Resource* resource = MessageLoopResource::GetCurrent();
   if (resource)
     return resource->GetReference();