[turbofan] Fix reduction of LoadProperty/StoreProperty to LoadNamed/StoreNamed.

test/mjsunit/compiler/named-store.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.
+
+function Foo(a, b) {
+  var bname = "b";
+  this["a"] = a;
+  this[bname] = b;
+  this.x = this.a + this.b;
+}
+
+var f1 = new Foo(3, 4);
+assertEquals(7, f1.x);
+
+// SMIs
+for (var i = 0; i < 6; i++) {
+  var f = new Foo(i, i + 2);
+  assertEquals(i + i + 2, f.x);
+}
+
+// derbles
+for (var i = 0.25; i < 6.25; i++) {
+  var f = new Foo(i, i + 2);
+  assertEquals(i + i + 2, f.x);
+}
+
+// stirngs
+for (var i = 0; i < 6; i++) {
+  var f = new Foo(i + "", (i + 2) + "");
+  assertEquals((i + "") + ((i + 2) + ""), f.x);
+}