More consistent order of type caches

lib/src/compiler/type_utilities.dart

 // Copyright (c) 2015, 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.
 
-import 'dart:collection' show HashMap, HashSet;
+import 'dart:collection' show HashMap, HashSet, LinkedHashMap;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 
 import '../js_ast/js_ast.dart' as JS;
 import '../js_ast/js_ast.dart' show js;
 import 'js_names.dart' as JS;
 
 Set<TypeParameterElement> freeTypeParameters(DartType t) {
   var result = new HashSet<TypeParameterElement>();
@@ skipping 10 matching lines @@
     }
   }
   find(t);
   return result;
 }
 
 /// _CacheTable tracks cache variables for variables that
 /// are emitted in place with a hoisted variable for a cache.
 class _CacheTable {
   /// Mapping from types to their canonical names.
-  final _names = new HashMap<DartType, JS.TemporaryId>();
+  // Use a LinkedHashMap to maintain key insertion order so the generated code
+  // is stable under slight perturbation.  (If this is not good enough we could
+  // sort by name to canonicalize order.)
+  final _names = new LinkedHashMap<DartType, JS.TemporaryId>();
   Iterable<DartType> get keys => _names.keys.toList();
 
   JS.Statement _dischargeType(DartType type) {
     var name = _names.remove(type);
     if (name != null) {
       return js.statement('let #;', [name]);
     }
     return null;
   }
 
@@ skipping 173 matching lines @@
     assert(hoistType != null);
     var table = hoistType
         ? (definite ? _definiteGenerators : _generators)
         : (definite ? _definiteCacheNames : _cacheNames);
     if (!table.isNamed(type)) {
       if (recordScopeDependencies(type)) return typeRep;
     }
     return table.nameType(type, typeRep);
   }
 }