PromiseThen should ignore non-function parameters.

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 ba5a306f84a23ecee98f11ddb1b1991afd394f1e..8575ba15ea885c4f7f1bb58c87409d772d6ccb98 100644
--- a/test/mjsunit/es6/promises.js
+++ b/test/mjsunit/es6/promises.js
@@ -399,6 +399,30 @@ function assertAsyncDone(iteration) {
 (function() {
   var deferred = Promise.defer()
   var p1 = deferred.promise
+  var p2 = p1.then(1, 2)
+  p2.then(
+    function(x) { assertAsync(x === 5, "then/resolve-non-function") },
+    assertUnreachable
+  )
+  deferred.resolve(5)
+  assertAsyncRan()
+})();
+
+(function() {
+  var deferred = Promise.defer()
+  var p1 = deferred.promise
+  var p2 = p1.then(1, 2)
+  p2.then(
+    assertUnreachable,
+    function(x) { assertAsync(x === 5, "then/reject-non-function") }
+  )
+  deferred.reject(5)
+  assertAsyncRan()
+})();
+
+(function() {
+  var deferred = Promise.defer()
+  var p1 = deferred.promise
   var p2 = {then: function(onResolve, onReject) { onResolve(p1) }}
   var p3 = Promise.accept(p2)
   p3.chain(