Harden internal uses of .chain

test/mjsunit/es6/promises.js

Index: test/mjsunit/es6/promises.js
diff --git a/test/mjsunit/es6/promises.js b/test/mjsunit/es6/promises.js
index 48b96f626f2ef2d9be3de9263d89885fd3dd3bb8..ba5a306f84a23ecee98f11ddb1b1991afd394f1e 100644
--- a/test/mjsunit/es6/promises.js
+++ b/test/mjsunit/es6/promises.js
@@ -790,11 +790,11 @@ function assertAsyncDone(iteration) {
 
   log = ""
   Promise.all([11, Promise.accept(12), 13, MyPromise.accept(14), 15, 16])
-  assertTrue(log === "nx14cn", "subclass/all/arg")
+  assertTrue(log === "nx14n", "subclass/all/arg")
 
   log = ""
   MyPromise.all([21, Promise.accept(22), 23, MyPromise.accept(24), 25, 26])
-  assertTrue(log === "nx24nnx21cnnx23cncnnx25cnnx26cn", "subclass/all/self")
+  assertTrue(log === "nx24nnx21nnx23nnnx25nnx26n", "subclass/all/self")
 })();