[modules] Teach JSObject::ReferencesObject about module contexts.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 5e2434ac36c0939e2ddbd343035c74c38a78b156..caa6996a824c3acb3492c0f5eb02bdff65056409 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -7387,7 +7387,8 @@ bool JSObject::ReferencesObject(Object* obj) {
     }
 
     // Check the context extension (if any) if it can have references.
-    if (context->has_extension() && !context->IsCatchContext()) {
+    if (context->has_extension() && !context->IsCatchContext() &&
+        !context->IsModuleContext()) {
       // With harmony scoping, a JSFunction may have a script context.
       // TODO(mvstanton): walk into the ScopeInfo.
       if (context->IsScriptContext()) {