Move some core classes to collection library.

tests/corelib/map_from_test.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 map.from.test;
+import 'dart:collection';
+
 main() {
   testWithConstMap();
   testWithNonConstMap();
   testWithLinkedMap();
 }
 
 testWithConstMap() {
   var map = const { 'b': 42, 'a': 43 };
   var otherMap = new Map.from(map);
   Expect.isTrue(otherMap is Map);
@@ skipping 53 matching lines @@
   var map = const { 'b': 1, 'a': 2, 'c': 3 };
   var otherMap = new LinkedHashMap.from(map);
   Expect.isTrue(otherMap is Map);
   Expect.isTrue(otherMap is HashMap);
   Expect.isTrue(otherMap is LinkedHashMap);
   var i = 1;
   for (var val in map.values) {
     Expect.equals(i++, val);
   }
 }