[turbofan] Fix known issue about computed property names.

test/mjsunit/harmony/computed-property-names-deopt.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: --harmony-computed-property-names --allow-natives-syntax
+
+
+(function TestProtoDeopt() {
+  var proto = {};
+
+  function deoptMe() {
+    %DeoptimizeFunction(f);
+    return proto;
+  }
+
+  function checkObject(name, value, o) {
+    assertSame(proto, Object.getPrototypeOf(o));
+    assertTrue(o.hasOwnProperty(name));
+    assertEquals(value, o[name]);
+  }
+
+  function f(name, value) {
+    return { [name]: value, __proto__: deoptMe() };
+  }
+
+  checkObject("a", 1, f("a", 1));
+  checkObject("b", 2, f("b", 2));
+  %OptimizeFunctionOnNextCall(f);
+  checkObject("c", 3, f("c", 3));
+})();