Revert "Remove deprecated mappedBy."

sdk/lib/_collection_dev/list.dart

 // Copyright (c) 2013, 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.dev;
 
 /**
  * Class implementing the read-operations on [List].
  *
  * Implements all read-only operations, except [:operator[]:] and [:length:],
@@ skipping 79 matching lines @@
     for (int i = 0; i < length; i++) {
       result.add(this[start + i]);
     }
     return result;
   }
 
   Iterable map(f(E element)) {
     return new MappedIterable(this, f);
   }
 
+  List mappedBy(f(E element)) {
+    return new MappedList(this, f);
+  }
+
   Iterable<E> take(int n) {
     return new SubListIterable(this, 0, n);
   }
 
   Iterable<E> skip(int n) {
     return new SubListIterable(this, n, null);
   }
 
   Iterable<E> get reversed => new ReversedListIterable(this);
 
@@ skipping 165 matching lines @@
     throw new UnsupportedError(
         "Cannot remove from an unmodifiable list");
   }
 
   void insertRange(int start, int length, [E initialValue]) {
     throw new UnsupportedError(
         "Cannot insert range in an unmodifiable list");
   }
 }
 
+class MappedList<S, T> extends UnmodifiableListBase<T> {
+  final List<S> _list;
+  // TODO(ahe): Restore type when feature is implemented in dart2js
+  // checked mode. http://dartbug.com/7733
+  final /* _Transformation<S, T> */ _f;
+
+  MappedList(this._list, T this._f(S element));
+
+  T operator[](int index) => _f(_list[index]);
+  int get length => _list.length;
 }
 
 /** An empty fixed-length list. */
 class EmptyList<E> extends FixedLengthListBase<E> {
   int get length => 0;
   E operator[](int index) { throw new RangeError.value(index); }
   void operator []=(int index, E value) { throw new RangeError.value(index); }
   Iterable<E> skip(int count) => const EmptyIterable();
   Iterable<E> take(int count) => const EmptyIterable();
   Iterable<E> get reversed => const EmptyIterable();
   void sort([int compare(E a, E b)]) {}
 }
 
 class ReversedListIterable<E> extends ListIterable<E> {
   Iterable<E> _source;
   ReversedListIterable(this._source);
 
   int get length => _source.length;
 
   E elementAt(int index) => _source.elementAt(_source.length - 1 - index);
 }