dart2js cps: Refactor and optimize string concatenations.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.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.cps_ir.shrinking_reductions;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /**
@@ skipping 539 matching lines @@
     node.receiver.parent = node;
     node.continuation.parent = node;
     node.arguments.forEach((Reference ref) => ref.parent = node);
   }
 
   processInvokeConstructor(InvokeConstructor node) {
     node.continuation.parent = node;
     node.arguments.forEach((Reference ref) => ref.parent = node);
   }
 
-  processConcatenateStrings(ConcatenateStrings node) {
-    node.continuation.parent = node;
-    node.arguments.forEach((Reference ref) => ref.parent = node);
-  }
-
   processBranch(Branch node) {
     node.condition.parent = node;
     node.trueContinuation.parent = node;
     node.falseContinuation.parent = node;
   }
 
   processTypeCast(TypeCast node) {
     node.typeArguments.forEach((Reference ref) => ref.parent = node);
     node.continuation.parent = node;
     node.value.parent = node;
@@ skipping 150 matching lines @@
   }
 
   String toString() => "$kind: $node";
 }
 
 /// A dummy class used solely to mark nodes as deleted once they are removed
 /// from a term.
 class _DeletedNode extends Node {
   accept(_) => null;
 }