Add unit test for regression in GVN caused by field type tracking.

BUG=v8:3347
LOG=n
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/333273004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21858 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/mjsunit/regress/regress-gvn-ftt.js

+// Copyright 2014 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --allow-natives-syntax --track-field-types --use-gvn
+
+function A(id) {
+  this.id = id;
+}
+
+var a1 = new A(1);
+var a2 = new A(2);
+
+
+var g;
+function f(o, value) {
+  g = o.o;
+  o.o = value;
+  return o.o;
+}
+
+var obj = {o: a1};
+
+f(obj, a1);
+f(obj, a1);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(a2.id, f(obj, a2).id);