[turbofan] Add test case for stores to properties that are also present on prototype.

R=verwaest@chromium.org
BUG=v8:4470
LOG=n

Review URL: https://codereview.chromium.org/1407233006

Cr-Commit-Position: refs/heads/master@{#31517}

test/mjsunit/compiler/regress-4470-1.js

+// Copyright 2015 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
+
+function Foo() {}
+Foo.prototype.x = 0;
+function foo(f) {
+  f.x = 1;
+}
+foo(new Foo);
+foo(new Foo);
+%OptimizeFunctionOnNextCall(foo);
+foo(new Foo);
+assertEquals(Foo.prototype.x, 0);