Move some core classes to collection library.

tests/corelib/linked_hash_map_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.
 
 // Dart test for linked hash-maps.
+library linkedHashMap.test;
+import 'dart:collection' show LinkedHashMap;
 
 class LinkedHashMapTest {
   static void testMain() {
     Map map = new LinkedHashMap();
     map["a"] = 1;
     map["b"] = 2;
     map["c"] = 3;
     map["d"] = 4;
     map["e"] = 5;
 
@@ skipping 88 matching lines @@
 
     clear();
     map.values.forEach(testForEachValue);
     verifyValues(valuesAfterAUpdate);
   }
 }
 
 main() {
   LinkedHashMapTest.testMain();
 }