dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.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 tree_ir_tracer;
 
 import 'dart:async' show EventSink;
 import '../tracer.dart';
 import 'tree_ir_nodes.dart';
 
@@ skipping 367 matching lines @@
     if (node.target.name.isEmpty) {
       callName = '${className}';
     } else {
       callName = '${className}.${node.target.name}';
     }
     String args = formatArguments(node);
     String keyword = node.constant != null ? 'const' : 'new';
     return "$keyword $callName($args)";
   }
 
-  String visitConcatenateStrings(ConcatenateStrings node) {
-    String args = node.arguments.map(visitExpression).join(', ');
-    return "concat [$args]";
-  }
-
   String visitLiteralList(LiteralList node) {
     String values = node.values.map(visitExpression).join(', ');
     return "list [$values]";
   }
 
   String visitLiteralMap(LiteralMap node) {
     List<String> entries = new List<String>();
     node.entries.forEach((LiteralMapEntry entry) {
       String key = visitExpression(entry.key);
       String value = visitExpression(entry.value);
@@ skipping 147 matching lines @@
       String prefix = v.element == null ? 'v' : '${v.element.name}_';
       while (name == null || _usedNames.contains(name)) {
         name = "$prefix${_counter++}";
       }
       _names[v] = name;
       _usedNames.add(name);
     }
     return name;
   }
 }