Fixes improper boxing in obj.dynamic

frog/lib/corelib.dart

 // Copyright (c) 2011, 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.
 
 #library("dart:core");
 #import("dart:coreimpl");
 
 // TODO(jimhug): Better way to map in standard corelib
 #source("../../corelib/src/bool.dart");
 #source("../../corelib/src/collection.dart");
@@ skipping 100 matching lines @@
 
 // Dart core library.
 
 class Object native "Object" {
 
   const Object() native;
 
   bool operator ==(Object other) native;
   String toString() native;
 
-  // TODO(jmesserly): optimize this. No need to call it.
-  get dynamic() => this;
+  // TODO(jmesserly): optimize this. No need to call it, unless it's overridden.
+  // Notes: "use strict" prevents boxing.
+  // The Dart "return this" might help with type inference.
+  get dynamic() native '"use strict"; return this;' { return this; }
 
   // TODO(jmesserly): add named args. For now stay compatible with the VM.
   noSuchMethod(String name, List args) {
     throw new NoSuchMethodException(this, name, args);
   }
 }
 
 LinkedHashMapImplementation _map(List itemsAndKeys) {
   LinkedHashMapImplementation ret = new LinkedHashMapImplementation();
   for (int i=0; i < itemsAndKeys.length;) {
     ret[itemsAndKeys[i++]] = itemsAndKeys[i++];
   }
   return ret;
 }
 
 ImmutableMap _constMap(List itemsAndKeys) {
   return new ImmutableMap(itemsAndKeys);
 }
 
 void _assert(var test, String text, String url, int line, int column) {
   if (test is Function) test = test();
   if (!test) throw new AssertionError._internal(text, url, line, column);
 }