Add test case for Promise .then() override

tests/ecmascript/test-bi-promise-proto-then-override.js

@@ -0,0 +1,36 @@
+/*---
+{
+    "skip": true
+}
+---*/
+
+/*===
+overridden then() called
+overridden then() called
+done
+then fulfill 1: 123
+then reject 2: aiee
+===*/
+
+// Promise.prototype.then() may be overridden, which affects some opportunities
+// for optimization.
+
+var oldThen = Promise.prototype.then;
+Promise.prototype.then = function (onFulfilled, onRejected) {
+    print('overridden then() called');
+    return oldThen.call(this, onFulfilled, onRejected);
+}
+
+var P = Promise.resolve(123);
+P.then(function (v) {
+    print('then fulfill 1:', v);
+    throw 'aiee';
+}, function (e) {
+    print('then reject 1:', String(e));
+}).then(function (v) {
+    print('then fulfill 2:', v);
+}, function (e) {
+    print('then reject 2:', String(e));
+});
+
+print('done');