Skip stack trace formatting in case the global object is already dead.

src/handles.h

Index: src/handles.h
diff --git a/src/handles.h b/src/handles.h
index 684f4ca38e758110b73eb07eabc0b497613bb024..ce281300e42c9bef5cfc26b2c1c6efc3979dccde 100644
--- a/src/handles.h
+++ b/src/handles.h
@@ -278,11 +278,12 @@ v8::Handle<v8::Array> GetKeysForIndexedInterceptor(Handle<JSReceiver> receiver,
 enum KeyCollectionType { LOCAL_ONLY, INCLUDE_PROTOS };
 
 // Computes the enumerable keys for a JSObject. Used for implementing
-// "for (n in object) { }".
+// "for (n in object) { }".  The side-effect free version omits getting keys
+// if it would trigger side effects.
+template<bool allow_side_effect>
 Handle<FixedArray> GetKeysInFixedArrayFor(Handle<JSReceiver> object,
                                           KeyCollectionType type,
                                           bool* threw);
-Handle<JSArray> GetKeysFor(Handle<JSReceiver> object, bool* threw);
 Handle<FixedArray> ReduceFixedArrayTo(Handle<FixedArray> array, int length);
 Handle<FixedArray> GetEnumPropertyKeys(Handle<JSObject> object,
                                        bool cache_result);