PPAPI: Add unlocking for PPP calls and callbacks. Add more locking.

ppapi/proxy/ppp_instance_private_proxy_unittest.cc

Index: ppapi/proxy/ppp_instance_private_proxy_unittest.cc
diff --git a/ppapi/proxy/ppp_instance_private_proxy_unittest.cc b/ppapi/proxy/ppp_instance_private_proxy_unittest.cc
index 6b87f1245728f144b50566f3a53414e207911c0e..957a3a7ad87fb3c2e837d91aa1f789d5f59f3faf 100644
--- a/ppapi/proxy/ppp_instance_private_proxy_unittest.cc
+++ b/ppapi/proxy/ppp_instance_private_proxy_unittest.cc
@@ -58,7 +58,7 @@ PP_Var GetInstanceObject(PP_Instance /*instance*/) {
   // The 1 ref we got from CreateObject will be passed to the host. We want to
   // have a ref of our own.
   printf("GetInstanceObject called\n");
-  PpapiGlobals::Get()->GetVarTracker()->AddRefVar(instance_obj);
+  plugin_var_deprecated_if()->AddRef(instance_obj);
   return instance_obj;
 }