[crankshaft] For-in index increment cannot overflow.

test/mjsunit/regress/regress-3650-1.js

+// Copyright 2016 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 --deopt-every-n-times=55
+// Flags: --nodead-code-elimination
+
+function f(t) {
+  var result = [];
+  for (var i in t) {
+    for (var j in t) {
+      result.push(i + j + t[i] + t[j]);
+      continue;
+    }
+  }
+  return result.join('');
+}
+
+var t = {a: "1", b: "2"};
+assertEquals("aa11ab12ba21bb22", f(t));
+%OptimizeFunctionOnNextCall(f);
+assertEquals("aa11ab12ba21bb22", f(t));