Remove deprecated Strings class.

tools/dom/scripts/idlrenderer.dart

 // Copyright (c) 2011, 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.
 
 List sorted(Iterable input, [compare, key]) {
   comparator(compare, key) {
     if (compare == null && key == null)
       return (a, b) => a.compareTo(b);
     if (compare == null)
       return (a, b) => key(a).compareTo(key(b));
@@ skipping 93 matching lines @@
           w('@$name');
         } else {
           var formattedArgs = [];
           for (var argName in sorted(args.keys)) {
             var argValue = args[argName];
             if (argValue == null)
               formattedArgs.add(argName);
             else
               formattedArgs.add('$argName=$argValue');
           }
-          w('@$name(${Strings.join(formattedArgs,',')})');
+          w('@$name(${formattedArgs.join(',')})');
         }
         w(' ');
       }
     } else if (node is IDLExtAttrs) {
       if(!node.map.isEmpty) {
         w('[');
         var sep = null;
         for (var name in sorted(node.map.keys)) {
           w(sep);
           sep = ', ';
@@ skipping 44 matching lines @@
       w(node.arguments, ', ');
       w(')');
     } else if (node is IDLTypeDef) {
       wln('typedef ${node.type.id} ${node.id};');
     } else {
       w('// $node\n');
     }
   };
 
   w(idl_node);
-  return Strings.concatAll(output);
+  return output.join();
 }