dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes_sexpr.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.
 
 library dart2js.ir_nodes_sexpr;
 
 import '../constants/values.dart';
 import '../util/util.dart';
 import 'cps_ir_nodes.dart';
 
@@ skipping 155 matching lines @@
     if (node.target.name.isEmpty) {
       callName = '${className}';
     } else {
       callName = '${className}.${node.target.name}';
     }
     String cont = access(node.continuation);
     String args = formatArguments(node);
     return '$indentation(InvokeConstructor $callName $args $cont)';
   }
 
-  String visitConcatenateStrings(ConcatenateStrings node) {
-    String cont = access(node.continuation);
-    String args = node.arguments.map(access).join(' ');
-    return '$indentation(ConcatenateStrings ($args) $cont)';
-  }
-
   String visitInvokeContinuation(InvokeContinuation node) {
     String name = access(node.continuation);
     if (node.isRecursive) name = 'rec $name';
     String args = node.arguments.map(access).join(' ');
     return '$indentation(InvokeContinuation $name ($args))';
   }
 
   String visitThrow(Throw node) {
     String value = access(node.value);
     return '$indentation(Throw $value)';
@@ skipping 267 matching lines @@
   void setReturnContinuation(Continuation node) {
     assert(!_names.containsKey(node) || _names[node] == 'return');
     _names[node] = 'return';
   }
 
   String getName(Node node) {
     if (!_names.containsKey(node)) return 'MISSING_NAME';
     return _names[node];
   }
 }