Convert resources to take an instance key instead of an Instance*.

ppapi/cpp/private/instance_private.cc

Index: ppapi/cpp/private/instance_private.cc
diff --git a/ppapi/cpp/private/instance_private.cc b/ppapi/cpp/private/instance_private.cc
index ad6e1a22e8ba5c54fcbc24bf61f5a276a5270f61..4e381149d7d3b50a388db2145b331a1f4de4e798 100644
--- a/ppapi/cpp/private/instance_private.cc
+++ b/ppapi/cpp/private/instance_private.cc
@@ -50,14 +50,14 @@ Var InstancePrivate::GetInstanceObject() {
 VarPrivate InstancePrivate::GetWindowObject() {
   if (!has_interface<PPB_Instance_Private>())
     return VarPrivate();
-  return VarPrivate(Var::PassRef(),
+  return VarPrivate(PASS_REF,
       get_interface<PPB_Instance_Private>()->GetWindowObject(pp_instance()));
 }
 
 VarPrivate InstancePrivate::GetOwnerElementObject() {
   if (!has_interface<PPB_Instance_Private>())
     return VarPrivate();
-  return VarPrivate(Var::PassRef(),
+  return VarPrivate(PASS_REF,
       get_interface<PPB_Instance_Private>()->GetOwnerElementObject(
           pp_instance()));
 }
@@ -65,7 +65,7 @@ VarPrivate InstancePrivate::GetOwnerElementObject() {
 VarPrivate InstancePrivate::ExecuteScript(const Var& script, Var* exception) {
   if (!has_interface<PPB_Instance_Private>())
     return VarPrivate();
-  return VarPrivate(Var::PassRef(),
+  return VarPrivate(PASS_REF,
              get_interface<PPB_Instance_Private>()->ExecuteScript(
                  pp_instance(),
                  script.pp_var(),