Use artificial hashCode values.

pkg/analyzer/lib/src/generated/utilities_general.dart

 // Copyright (c) 2014, 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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.utilities.general;
 
 import 'dart:profiler';
@@ skipping 10 matching lines @@
   }
 
   static int finish(int hash) {
     hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3));
     hash = hash ^ (hash >> 11);
     return 0x1fffffff & (hash + ((0x00003fff & hash) << 15));
   }
 
   static int hash2(a, b) => finish(combine(combine(0, a), b));
 
+  static int hash3(a, b, c) => finish(combine(combine(combine(0, a), b), c));

[Brian Wilkerson, 2015/05/23 15:58:50]

Perhaps something more general would be better (although it wouldn't be as
performant):

static int hash(List<int> hashCodes) {
  int result = 0;
  for (int hashCode in hashCodes) {
    result = combine(result, hashCode);
  }
  return result;
}

+
   static int hash4(a, b, c, d) =>
       finish(combine(combine(combine(combine(0, a), b), c), d));
 }
 
 /**
  * Helper class for gathering performance statistics.  This class is modeled on
  * the UserTag class in dart:profiler so that it can interoperate easily with
  * it.
  */
 abstract class PerformanceTag {
@@ skipping 105 matching lines @@
 
   makeCurrentWhile(f()) {
     PerformanceTag prevTag = makeCurrent();
     try {
       return f();
     } finally {
       prevTag.makeCurrent();
     }
   }
 }