Use relative URIs for core library part-of statements.

sdk/lib/collection/maps.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.collection;
+part of "collection.dart";
 
 /**
  * Base class for implementing a [Map].
  *
  * This class has a basic implementation of all but five of the members of
  * [Map].
  * A basic `Map` class can be implemented by extending this class and
  * implementing `keys`, `operator[]`, `operator[]=`, `remove` and `clear`.
  * The remaining operations are implemented in terms of these five.
  *
@@ skipping 350 matching lines @@
       map[keyIterator.current] = valueIterator.current;
       hasNextKey = keyIterator.moveNext();
       hasNextValue = valueIterator.moveNext();
     }
 
     if (hasNextKey || hasNextValue) {
       throw new ArgumentError("Iterables do not have same length.");
     }
   }
 }