dart2js cps: Use a global counter to generate hash codes.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

 // Copyright (c) 2013, 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.ir_nodes;
 
 import '../constants/values.dart' as values show ConstantValue;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
 import '../elements/elements.dart';
 import '../io/source_information.dart' show SourceInformation;
 import '../types/types.dart' show TypeMask;
 import '../universe/universe.dart' show Selector;
 
 import 'builtin_operator.dart';
 export 'builtin_operator.dart';
 
 // These imports are only used for the JavaScript specific nodes.  If we want to
 // support more than one native backend, we should probably create better
 // abstractions for native code and its type and effect system.
 import '../js/js.dart' as js show Template;
 import '../native/native.dart' as native show NativeBehavior;
 
 abstract class Node {
   /// A pointer to the parent node. Is null until set by optimization passes.
   Node parent;
 
+  /// Workaround for a slow Object.hashCode in the VM.
+  static int _usedHashCodes = 0;
+  final int hashCode = ++_usedHashCodes;
+
   accept(Visitor visitor);
 }
 
 /// Expressions can be evaluated, and may diverge, throw, and/or have
 /// side-effects.
 ///
 /// Evaluation continues by stepping into a sub-expression, invoking a
 /// continuation, or throwing an exception.
 ///
 /// Expressions do not a return value. Expressions that produce values should
@@ skipping 1589 matching lines @@
 /// Visit a just-deleted subterm and unlink all [Reference]s in it.
 class RemovalVisitor extends RecursiveVisitor {
   processReference(Reference reference) {
     reference.unlink();
   }
 
   static void remove(Node node) {
     (new RemovalVisitor()).visit(node);
   }
 }