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

ppapi/cpp/resource.cc

Index: ppapi/cpp/resource.cc
diff --git a/ppapi/cpp/resource.cc b/ppapi/cpp/resource.cc
index 5a327d635937daabb1c46d90a5108bdc2f37df04..3ccc198b3b116ac7e842fd9f53bcb91032c0c7cb 100644
--- a/ppapi/cpp/resource.cc
+++ b/ppapi/cpp/resource.cc
@@ -44,6 +44,9 @@ Resource::Resource(PP_Resource resource) : pp_resource_(resource) {
     Module::Get()->core()->AddRefResource(pp_resource_);
 }
 
+Resource::Resource(PassRef, PP_Resource resource) : pp_resource_(resource) {
+}
+
 void Resource::PassRefFromConstructor(PP_Resource resource) {
   PP_DCHECK(!pp_resource_);
   pp_resource_ = resource;