Use relative URIs for core library part-of statements.

sdk/lib/_internal/js_runtime/lib/constant_map.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 _js_helper;
+part of "js_helper.dart";
 
 class ConstantMapView<K, V> extends UnmodifiableMapView implements ConstantMap {
   ConstantMapView(Map base) : super(base);
 }
 
 abstract class ConstantMap<K, V> implements Map<K, V> {
   // Used to create unmodifiable maps from other maps.
   factory ConstantMap.from(Map other) {
     List keys = other.keys.toList();
     bool allStrings = true;
@@ skipping 166 matching lines @@
   Iterable<K> get keys {
     return _getMap().keys;
   }
 
   Iterable<V> get values {
     return _getMap().values;
   }
 
   int get length => _getMap().length;
 }