Reland of [runtime] Do not use the enum-cache for non-prototype objects.

test/mjsunit/regress/regress-705-shadowed_properties.js

+// 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.
+
+function allKeys(object) {
+  var keys = [];
+  for (var key in object) {
+    keys.push(key);
+  }
+  return keys;
+}
+
+var a = { a1: true, a2: true};
+var b = { b1: true, b2: true};
+a.__proto__ = b;
+
+assertEquals(['a1', 'a2', 'b1', 'b2'], allKeys(a));
+assertEquals(['b1', 'b2'], allKeys(b));
+
+// Adding a non-enumerable property to either a or b shouldn't change
+// the result.
+var propertyDescriptor = {
+  enumerable: false,
+  configurable: true,
+  writable: true,
+  value: true
+};
+
+Object.defineProperty(a, 'a3', propertyDescriptor);
+assertEquals(['a1', 'a2', 'b1', 'b2'], allKeys(a));
+assertEquals(['b1', 'b2'], allKeys(b));
+
+Object.defineProperty(b, 'b3', propertyDescriptor);
+assertEquals(['a1', 'a2', 'b1', 'b2'], allKeys(a));
+assertEquals(['b1', 'b2'], allKeys(b));
+
+// A non-enumerable property shadows an enumerable version on the prototype
+// chain.
+b['a3'] = true;
+assertEquals(['a1', 'a2', 'b1', 'b2'], allKeys(a));
+assertEquals(['b1', 'b2', 'a3'], allKeys(b));
+
+// Try the same with indexed-properties.
+var aIndex  = {0:true, 1:true};
+var bIndex = {10:true, 11:true};
+aIndex.__proto__= bIndex;
+assertEquals(['0', '1', '10', '11'], allKeys(aIndex));
+assertEquals(['10', '11'], allKeys(bIndex));
+
+Object.defineProperty(aIndex, 2, propertyDescriptor);
+Object.defineProperty(bIndex, 12, propertyDescriptor);
+assertEquals(['0', '1', '10', '11'], allKeys(aIndex));
+assertEquals(['10', '11'], allKeys(bIndex));
+
+bIndex[2] = 2;
+assertEquals(['0', '1', '10', '11'], allKeys(aIndex));
+assertEquals(['2', '10', '11'], allKeys(bIndex));