Use relative URIs for core library part-of statements.

sdk/lib/core/object.dart

 // Copyright (c) 2012, 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.
 
-part of dart.core;
+part of "core.dart";
 
 /**
  * The base class for all Dart objects.
  *
  * Because Object is the root of the Dart class hierarchy,
  * every other Dart class is a subclass of Object.
  *
  * When you define a class, you should override [toString]
  * to return a string describing an instance of that class.
  * You might also need to define [hashCode] and [==], as described in the
@@ skipping 88 matching lines @@
    *
    * The default behavior is to throw a [NoSuchMethodError].
    */
   external dynamic noSuchMethod(Invocation invocation);
 
   /**
    * A representation of the runtime type of the object.
    */
   external Type get runtimeType;
 }