[es6] Reintroduce the instanceof operator in the backends.

test/mjsunit/compiler/optimized-instanceof-1.js

Index: test/mjsunit/compiler/optimized-instanceof-1.js
diff --git a/test/mjsunit/compiler/optimized-instanceof-1.js b/test/mjsunit/compiler/optimized-instanceof-1.js
new file mode 100644
index 0000000000000000000000000000000000000000..538b0ef524eca11cae85cf8772a95e7e5ebb11a8
--- /dev/null
+++ b/test/mjsunit/compiler/optimized-instanceof-1.js
@@ -0,0 +1,17 @@
+// 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 --harmony-instanceof
+
+function F() {}
+var f = new F
+
+var proto = Object.getPrototypeOf(F);
+Object.setPrototypeOf(F, null);
+F[Symbol.hasInstance] = function(v) { return true };
+Object.setPrototypeOf(F, proto);
+
+function foo(x) { return x instanceof F };
+%OptimizeFunctionOnNextCall(foo);
+assertTrue(foo(1));