Convert String and List to abstract classes.

lib/coreimpl/collections.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.
 
 /**
  * The [Collections] class implements static methods useful when
  * writing a class that implements [Collection] and the [iterator]
  * method.
  */
 class Collections {
@@ skipping 18 matching lines @@
   }
 
   static List map(Iterable source, List destination, f(o)) {
     for (final e in source) {
       destination.add(f(e));
     }
     return destination;
   }
 
   static Dynamic reduce(Iterable iterable,
-                        Dynamic initialValue,
-                        Dynamic combine(Dynamic previousValue, element)) {
+                        var initialValue,
+                        Dynamic combine(var previousValue, element)) {
     for (final element in iterable) {
       initialValue = combine(initialValue, element);
     }
     return initialValue;
   }
 
   static List filter(Iterable source, List destination, bool f(o)) {
     for (final e in source) {
       if (f(e)) destination.add(e);
     }
@@ skipping 95 matching lines @@
    * Returns true if the specified collection contains the specified object
    * reference.
    */
   static _containsRef(Collection c, Object ref) {
     for (var e in c) {
       if (e === ref) return true;
     }
     return false;
   }
 }