dart2js cps: Maintain parent pointers instead of recomputing them.

tests/compiler/dart2js/js_backend_cps_ir_source_information_test.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.
 
 // Test that the CPS IR code generator generates source information.
 
 library source_information_tests;
 
 import 'package:async_helper/async_helper.dart';
 import 'package:expect/expect.dart';
@@ skipping 105 matching lines @@
 class JsSourceInformationVisitor extends js.BaseVisitor {
   List<String> sourceInformation = <String>[];
 
   @override
   visitCall(js.Call node) {
     sourceInformation.add('${node.sourceInformation}');
     super.visitCall(node);
   }
 }
 
-class IrSourceInformationVisitor extends ir.RecursiveVisitor {
+class IrSourceInformationVisitor extends ir.TrampolineRecursiveVisitor {
   List<String> sourceInformation = <String>[];
 
   @override
   processInvokeStatic(ir.InvokeStatic node) {
     sourceInformation.add('${node.sourceInformation}');
   }
 }
 
 const List<TestEntry> tests = const [
   const TestEntry("""
 main() { print('Hello World'); }
 """, const ['memory:test.dart:[1,10]']),
 const TestEntry("""
 main() {
   print('Hello');
   print('World');
 }
 """, const ['memory:test.dart:[2,3]',
             'memory:test.dart:[3,3]']),
 ];
 
 void main() {
   runTests(tests);
 }