Incorporate some code review comments.

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.
 
 // IrNodes are kept in a separate library to have precise control over their
 // dependencies on other parts of the system.
 library dart2js.ir_nodes;
 
 import '../constants/expressions.dart';
 import '../constants/values.dart' as values show ConstantValue;
@@ skipping 122 matching lines @@
 ///
 /// The bound continuations are in scope in the body and the continuation
 /// parameters are in scope in the respective continuation bodies.
 /// During one-pass construction a LetCont whose first continuation has an empty
 /// body is used to represent the one-level context
 /// 'let cont ... k(v) = [] ... in E'.
 class LetCont extends Expression implements InteriorNode {
   List<Continuation> continuations;
   Expression body;
 
-  LetCont(this.continuations, this.body);
+  LetCont(Continuation continuation, this.body)
+      : continuations = <Continuation>[continuation];
+
+  LetCont.many(this.continuations, this.body);
 
   Expression plug(Expression expr) {
     assert(continuations != null &&
            continuations.isNotEmpty &&
            continuations.first.body == null);
     return continuations.first.body = expr;
   }
 
   accept(Visitor visitor) => visitor.visitLetCont(this);
 }
@@ skipping 1157 matching lines @@
 
   void visitIdentical(Identical node) {
     visitReference(node.left);
     visitReference(node.right);
   }
 
   void visitInterceptor(Interceptor node) {
     visitReference(node.input);
   }
 }