dart2js cps: Maintain parent pointers instead of recomputing them.

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

Index: pkg/compiler/lib/src/cps_ir/remove_refinements.dart
diff --git a/pkg/compiler/lib/src/cps_ir/remove_refinements.dart b/pkg/compiler/lib/src/cps_ir/remove_refinements.dart
index 4d7aae3d847ccd9a76dd70788a1867e713e706dd..98f1c17a8867dd072bc56f7d1d30d89566f965a7 100644
--- a/pkg/compiler/lib/src/cps_ir/remove_refinements.dart
+++ b/pkg/compiler/lib/src/cps_ir/remove_refinements.dart
@@ -5,18 +5,16 @@
 library cps_ir.optimization.remove_refinements;
 
 import 'optimizers.dart' show Pass;
-import 'shrinking_reductions.dart' show ParentVisitor;
 import 'cps_ir_nodes.dart';
 
 /// Removes all [Refinement] nodes from the IR.
 ///
 /// This simplifies subsequent passes that don't rely on path-sensitive
 /// type information but depend on equality between primitives.
-class RemoveRefinements extends RecursiveVisitor implements Pass {
+class RemoveRefinements extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Remove refinement nodes';
 
   void rewrite(FunctionDefinition node) {
-    new ParentVisitor().visit(node);
     visit(node);
   }