dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.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.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /**
@@ skipping 370 matching lines @@
     _rewriteList(node.arguments);
     node.receiver = visitExpression(node.receiver);
     return node;
   }
 
   Expression visitInvokeConstructor(InvokeConstructor node) {
     _rewriteList(node.arguments);
     return node;
   }
 
-  Expression visitConcatenateStrings(ConcatenateStrings node) {
-    _rewriteList(node.arguments);
-    return node;
-  }
-
   Expression visitConditional(Conditional node) {
     // Conditional expressions do not exist in the input, but they are
     // introduced by if-to-conditional conversion.
     // Their subexpressions have already been processed; do not reprocess them.
     //
     // Note that this can only happen for conditional expressions. It is an
     // error for any other type of expression to be visited twice or to be
     // created and then visited. We use this special treatment of conditionals
     // to allow for assignment inlining after if-to-conditional conversion.
     //
@@ skipping 632 matching lines @@
   IsVariableUsedVisitor(this.variable);
 
   visitVariableUse(VariableUse node) {
     if (node.variable == variable) {
       wasFound = true;
     }
   }
 
   visitInnerFunction(FunctionDefinition node) {}
 }