More generic input type.

lib/compiler/implementation/dart_backend/backend.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.
 
 class DartBackend extends Backend {
   final List<CompilerTask> tasks;
 
   Map<Element, TreeElements> get resolvedElements() =>
       compiler.enqueuer.resolution.resolvedElements;
 
@@ skipping 165 matching lines @@
 
   void collect() {
     compiler.withCurrentElement(rootElement, () {
       rootElement.parseNode(compiler).accept(this);
     });
   }
 }
 
 compareBy(f) => (x, y) => f(x).compareTo(f(y));
 
-List sorted(List l, comparison) {
+List sorted(Iterable l, comparison) {
   final result = new List.from(l);
   result.sort(comparison);
   return result;
 }
 
 List<Element> sortElements(Collection<Element> elements) {
   compareElements(e0, e1) {
     int result = compareBy((e) => e.getLibrary().uri.toString())(e0, e1);
     if (result != 0) return result;
     return compareBy((e) => e.position().charOffset)(e0, e1);
   }
 
   return sorted(elements, compareElements);
 }