dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/cps_ir/cps_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 dart2js.ir_tracer;
 
 import 'dart:async' show EventSink;
 import 'cps_ir_nodes.dart' as cps_ir hide Function;
 import '../tracer.dart';
 
@@ skipping 157 matching lines @@
     if (node.target.name.isEmpty) {
       callName = '${className}';
     } else {
       callName = '${className}.${node.target.name}';
     }
     String args = node.arguments.map(formatReference).join(', ');
     String kont = formatReference(node.continuation);
     printStmt(dummy, "InvokeConstructor $callName ($args) $kont");
   }
 
-  visitConcatenateStrings(cps_ir.ConcatenateStrings node) {
-    String dummy = names.name(node);
-    String args = node.arguments.map(formatReference).join(', ');
-    String kont = formatReference(node.continuation);
-    printStmt(dummy, "ConcatenateStrings ($args) $kont");
-  }
-
   visitThrow(cps_ir.Throw node) {
     String dummy = names.name(node);
     String value = formatReference(node.value);
     printStmt(dummy, "Throw $value");
   }
 
   visitRethrow(cps_ir.Rethrow node) {
     String dummy = names.name(node);
     printStmt(dummy, "Rethrow");
   }
@@ skipping 301 matching lines @@
   }
 
   visitInvokeMethodDirectly(cps_ir.InvokeMethodDirectly exp) {
     addEdgeToContinuation(exp.continuation);
   }
 
   visitInvokeConstructor(cps_ir.InvokeConstructor exp) {
     addEdgeToContinuation(exp.continuation);
   }
 
-  visitConcatenateStrings(cps_ir.ConcatenateStrings exp) {
-    addEdgeToContinuation(exp.continuation);
-  }
-
   visitThrow(cps_ir.Throw exp) {
   }
 
   visitRethrow(cps_ir.Rethrow exp) {
   }
 
   visitUnreachable(cps_ir.Unreachable node) {
   }
 
   visitSetMutableVariable(cps_ir.SetMutableVariable exp) {
@@ skipping 97 matching lines @@
   visitCreateInvocationMirror(cps_ir.CreateInvocationMirror node) {
     unexpectedNode(node);
   }
   visitTypeTest(cps_ir.TypeTest node) {
     unexpectedNode(node);
   }
   visitApplyBuiltinOperator(cps_ir.ApplyBuiltinOperator node) {
     unexpectedNode(node);
   }
 }