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

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

Index: pkg/compiler/lib/src/cps_ir/parent_visitor.dart
diff --git a/pkg/compiler/lib/src/cps_ir/parent_visitor.dart b/pkg/compiler/lib/src/cps_ir/parent_visitor.dart
deleted file mode 100644
index 33896e0e834e96e7fd73b805f98d44c10d28590f..0000000000000000000000000000000000000000
--- a/pkg/compiler/lib/src/cps_ir/parent_visitor.dart
+++ /dev/null
@@ -1,43 +0,0 @@
-// 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 cps_ir.parent_visitor;
-
-import 'cps_ir_nodes.dart';
-
-/// Traverses the CPS term and sets node.parent for each visited node.
-class ParentVisitor extends DeepRecursiveVisitor {
-  static void setParents(Node node) {
-    ParentVisitor visitor = new ParentVisitor._make();
-    visitor._worklist.add(node);
-    visitor.trampoline();
-  }
-
-  /// Private to avoid accidental `new ParentVisitor().visit(node)` calls.
-  ParentVisitor._make();
-
-  Node _parent;
-  final List<Node> _worklist = <Node>[];
-
-  void trampoline() {
-    while (_worklist.isNotEmpty) {
-      _parent = _worklist.removeLast();
-      _parent.accept(this);
-    }
-  }
-
-  @override
-  visit(Node node) {
-    _worklist.add(node);
-    assert(_parent != node);
-    assert(_parent != null);
-    node.parent = _parent;
-  }
-
-  @override
-  processReference(Reference node) {
-    node.parent = _parent;
-  }
-}
-