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

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 7369 matching lines @@
           if (ctxobj->ReferencesObject(obj)) {
             return true;
           }
         } else if (ctxobj == obj) {
           return true;
         }
       }
     }
 
     // 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()) {
         return false;
       }
 
       return context->extension_object()->ReferencesObject(obj);
     }
   }
 
@@ skipping 13146 matching lines @@
       // not
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 }  // namespace internal
 }  // namespace v8