Incorporate some code review comments.

tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart

 // Copyright (c) 2014, 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.
 
 // SExpressionUnstringifier implements the inverse operation to
 // [SExpressionStringifier].
 
 library sexpr_unstringifier;
 
 import 'package:compiler/src/constants/expressions.dart'
@@ skipping 479 matching lines @@
     List<Continuation> continuations = <Continuation>[];
     while (tokens.current != ")") {
       continuations.add(parseContinuation());
     }
     tokens.consumeEnd();
 
     // body)
     Expression body = parseExpression();
     tokens.consumeEnd();
 
-    return new LetCont(continuations, body);
+    return new LetCont.many(continuations, body);
   }
 
   /// (SetClosureVariable name value body)
   SetClosureVariable parseSetClosureVariable() {
     tokens.consumeStart(SET_CLOSURE_VARIABLE);
 
     ClosureVariable local = name2variable[tokens.read()];
     Primitive value = name2variable[tokens.read()];
     assert(value != null);
 
@@ skipping 179 matching lines @@
     return new ReifyTypeVar(type);
   }
 
   /// (This)
   This parseThis() {
     tokens.consumeStart(THIS);
     tokens.consumeEnd();
     return new This();
   }
 }