Add EfficientLength marker interface to some iterabels.

sdk/lib/utf/utf.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.
 
 /**
  * Support for encoding and decoding Unicode characters in UTF-8, UTF-16, and
  * UTF-32.
  */
 @deprecated
 library dart.utf;
-import "dart:_collection-dev" show deprecated;
+import "dart:_collection-dev" show deprecated, EfficientLength;
 import "dart:async";
 import "dart:collection";
 part "utf_stream.dart";
 part "utf8.dart";
 part "utf16.dart";
 part "utf32.dart";
 
 // TODO(jmesserly): would be nice to have this on String (dartbug.com/6501).
 /**
  * *DEPRECATED*: Use `dart:convert` or `package:utf/utf.dart` instead.
@@ skipping 193 matching lines @@
   }
 }
 
 /**
  * _ListRange in an internal type used to create a lightweight Interable on a
  * range within a source list. DO NOT MODIFY the underlying list while
  * iterating over it. The results of doing so are undefined.
  */
 // TODO(floitsch): Consider removing the extend and switch to implements since
 // that's cheaper to allocate.
-class _ListRange extends IterableBase {
+class _ListRange extends IterableBase implements EfficientLength {
   final List _source;
   final int _offset;
   final int _length;
 
   _ListRange(source, [offset = 0, length]) :
       this._source = source,
       this._offset = offset,
       this._length = (length == null ? source.length - offset : length) {
     if (_offset < 0 || _offset > _source.length) {
       throw new RangeError.value(_offset);
@@ skipping 44 matching lines @@
     _offset -= by;
   }
 
   int get remaining => _end - _offset - 1;
 
   void skip([int count = 1]) {
     _offset += count;
   }
 }