Add another method write barrier regression test. no_r=me.

--HG--
extra : rebase_source : 4348354a9d97e5249f4442a0bfc9b61b0220cd4a

js/src/jit-test/tests/basic/testMethodWriteBarrier4.js

@@ -0,0 +1,12 @@
+var z = 0;
+function f() {
+    this.b = function() {};
+    this.b = undefined;
+    if (z++ > HOTLOOP)
+        this.b();
+}
+
+try {
+    for (var i = 0; i < HOTLOOP + 2; i++)
+        new f();
+} catch (exc) {}