Extend Iterable instead of implementing it.

sdk/lib/_internal/compiler/implementation/lib/regexp_helper.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.
 
 List regExpExec(JSSyntaxRegExp regExp, String str) {
   var nativeRegExp = regExpGetNative(regExp);
   var result = JS('List', r'#.exec(#)', nativeRegExp, str);
   if (JS('bool', r'# == null', result)) return null;
   return result;
 }
@@ skipping 102 matching lines @@
 
   List<String> groups(List<int> groups) {
     List<String> out = [];
     for (int i in groups) {
       out.add(group(i));
     }
     return out;
   }
 }
 
-class _AllMatchesIterable implements Iterable<Match> {
+class _AllMatchesIterable extends Iterable<Match> {
   final JSSyntaxRegExp _re;
   final String _str;
 
   const _AllMatchesIterable(this._re, this._str);
 
   Iterator<Match> iterator() => new _AllMatchesIterator(_re, _str);
 }
 
 class _AllMatchesIterator implements Iterator<Match> {
   final RegExp _re;
@@ skipping 26 matching lines @@
     // hidden global flag.
     _next = _re.firstMatch(_str);
     if (_next == null) {
       _done = true;
       return false;
     } else {
       return true;
     }
   }
 }