dart2js cps: Pull SetFields into field initializer arguments.

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

 // Copyright (c) 2013, 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.ir_nodes;
 
 import 'dart:collection';
 import 'cps_fragment.dart' show CpsFragment;
 import 'cps_ir_nodes_sexpr.dart';
 import '../constants/values.dart' as values;
 import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
@@ skipping 1993 matching lines @@
     }
     walkBlock(root);
     while (stack.isNotEmpty) {
       walkBlock(stack.removeLast());
     }
     nodes.reversed.forEach(v.visit);
   }
 
   /// Visits block-level nodes in lexical pre-order.
   ///
-  /// The IR may be transformed during the traversal, but the currently
-  /// visited node should not be removed, as its 'body' pointer is needed
-  /// for the traversal.
+  /// Traversal continues at the original success for the current node, so:
+  /// - The current node can safely be removed.
+  /// - Nodes inserted immediately below the current node will not be seen.
+  /// - The body of the current node should not be moved/removed, as traversal
+  ///   would otherwise continue into an orphaned or relocated node.
   static void traverseInPreOrder(FunctionDefinition root, BlockVisitor v) {
     List<Continuation> stack = <Continuation>[];
     void walkBlock(InteriorNode block) {
       v.visit(block);
       Expression node = block.body;
-      v.visit(node);
-      while (node.next != null) {
+      while (node != null) {
         if (node is LetCont) {
           stack.addAll(node.continuations);
         } else if (node is LetHandler) {
           stack.add(node.handler);
         }
-        node = node.next;
+        Expression next = node.next;
         v.visit(node);
+        node = next;
       }
     }
     walkBlock(root);
     while (stack.isNotEmpty) {
       walkBlock(stack.removeLast());
     }
   }
 }
 
 abstract class Visitor<T> implements BlockVisitor<T> {
@@ skipping 868 matching lines @@
     plug(new Branch.loose(_definitions.getCopy(node.condition),
         _copies[node.trueContinuation.definition],
         _copies[node.falseContinuation.definition])
       ..isStrictCheck = node.isStrictCheck);
   }
 
   visitUnreachable(Unreachable node) {
     plug(new Unreachable());
   }
 }