dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/tree_ir/optimization/pull_into_initializers.dart

 // Copyright (c) 2015, 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.pull_into_initializers;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /// Pulls assignment expressions to the top of the function body so they can be
@@ skipping 181 matching lines @@
     seenImpure = true;
     return node;
   }
 
   Expression visitInvokeConstructor(InvokeConstructor node) {
     rewriteList(node.arguments);
     seenImpure = true;
     return node;
   }
 
-  Expression visitConcatenateStrings(ConcatenateStrings node) {
-    rewriteList(node.arguments);
-    seenImpure = true;
-    return node;
-  }
-
   Expression visitTypeExpression(TypeExpression node) {
     rewriteList(node.arguments);
     return node;
   }
 
   Expression visitConditional(Conditional node) {
     node.condition = visitExpression(node.condition);
     if (seenImpure) return node;
     node.thenExpression = visitExpression(node.thenExpression);
     if (seenImpure) return node;
@@ skipping 106 matching lines @@
   Expression visitCreateInvocationMirror(CreateInvocationMirror node) {
     rewriteList(node.arguments);
     return node;
   }
 
   Expression visitApplyBuiltinOperator(ApplyBuiltinOperator node) {
     rewriteList(node.arguments);
     return node;
   }
 }