Turn keyed loads with string-based (non-convertible to array-index) key into named loads

test/mjsunit/keyed-named-access.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: --allow-natives-syntax
+
+var k = "x";
+var o1 = {x: 10};
+var o2 = {x: 11, y: 20};
+var o3 = {x: 12, y: 20, z: 100};
+
+function f(o) {
+  var result = 0;
+  for (var i = 0; i < 100; i++) {
+    result += o[k];
+  }
+  return result;
+}
+
+f(o1);
+f(o1);
+f(o1);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(1000, f(o1));
+
+f(o2);
+f(o2);
+f(o2);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(1100, f(o2));
+
+f(o3);
+f(o3);
+f(o3);
+%OptimizeFunctionOnNextCall(f);
+assertEquals(1200, f(o3));