Use relative URIs for core library part-of statements.

sdk/lib/collection/iterable.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";
 
 /**
  * This [Iterable] mixin implements all [Iterable] members except `iterator`.
  *
  * All other methods are implemented in terms of `iterator`.
  */
 abstract class IterableMixin<E> implements Iterable<E> {
   // This class has methods copied verbatim into:
   // - IterableBase
   // - SetMixin
@@ skipping 373 matching lines @@
       elision = "...";
       length += ELLIPSIS_SIZE + OVERHEAD;
     }
   }
   if (elision != null) {
     parts.add(elision);
   }
   parts.add(penultimateString);
   parts.add(ultimateString);
 }