Constrain type annotations with deferred types.

sdk/lib/_internal/compiler/implementation/util/util.dart

 // Copyright (c) 2011, 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.
 
 library dart2js.util;
 
 import "dart:collection";
 import 'util_implementation.dart';
 import 'characters.dart';
 
@@ skipping 278 matching lines @@
   buffer.write(string);
 }
 
 int computeHashCode(part1, [part2, part3, part4, part5]) {
   return (part1.hashCode
           ^ part2.hashCode
           ^ part3.hashCode
           ^ part4.hashCode
           ^ part5.hashCode) & 0x3fffffff;
 }
+
+class Pair<S, T> {
+  final S first;
+  final T second;
+  Pair(this.first, this.second);
+}