dart2js cps: Maintain parent pointers instead of recomputing them.

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

Index: pkg/compiler/lib/src/cps_ir/redundant_phi.dart
diff --git a/pkg/compiler/lib/src/cps_ir/redundant_phi.dart b/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
index 693b612d6858c901c18fec4f69a8858e74027ad8..183f8e36ff2e6fe9815e65b94389b4d851a62ccc 100644
--- a/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
+++ b/pkg/compiler/lib/src/cps_ir/redundant_phi.dart
@@ -15,16 +15,13 @@ import 'optimizers.dart';
 /// (except for feedback). Redundant parameters are removed from the
 /// continuation signature, all invocations, and replaced within the
 /// continuation body.
-class RedundantPhiEliminator extends RecursiveVisitor implements Pass {
+class RedundantPhiEliminator extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Redundant phi elimination';
 
   final Set<Continuation> workSet = new Set<Continuation>();
 
   @override
   void rewrite(FunctionDefinition root) {
-    // Set all parent pointers.
-    new ParentVisitor().visit(root);
-
     // Traverse the tree once to build the work set.
     visit(root);