Revert "dart2js cps: Maintain parent pointers instead of recomputing them."

pkg/compiler/lib/src/cps_ir/mutable_ssa.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.
 
 library dart2js.cps_ir.mutable_ssa;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /// Determines which mutable variables should be rewritten to phi assignments
 /// in this pass.
 ///
 /// We do not rewrite variables that have an assignment inside a try block that
 /// does not contain its declaration.
-class MutableVariablePreanalysis extends TrampolineRecursiveVisitor {
+class MutableVariablePreanalysis extends RecursiveVisitor {
   // Number of try blocks enclosing the current position.
   int currentDepth = 0;
 
   /// Number of try blocks enclosing the declaration of a given mutable
   /// variable.
   ///
   /// All mutable variables seen will be present in the map after the analysis.
   Map<MutableVariable, int> variableDepth = <MutableVariable, int>{};
 
   /// Variables with an assignment inside a try block that does not contain
@@ skipping 216 matching lines @@
 class VariableItem extends StackItem {}
 
 /// Represents a yet unprocessed continuation together with the
 /// environment in which to process it.
 class ContinuationItem extends StackItem {
   final Continuation continuation;
   final Map<MutableVariable, Primitive> environment;
 
   ContinuationItem(this.continuation, this.environment);
 }