Reapply "Implement an LRU cache in dart:_internal and use it for the getter/setter caches in the VM…

tests/lib/mirrors/lru_test.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:mirrors";
+import "lru_expect.dart";
+
+newLRUMapWithShift(int shift) {
+  var lib = currentMirrorSystem().libraries[Uri.parse("dart:_internal")];
+  var cls = lib.declarations[#LRUMap];
+  return cls.newInstance(#withShift, [shift]).reflectee;
+}
+
+main() {
+  expect(newLRUMapWithShift);
+}