Add Function based profile tree

runtime/observatory/lib/src/elements/script_ref.dart

 // Copyright (c) 2013, 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 script_ref_element;
 
 import 'package:polymer/polymer.dart';
 import 'package:observatory/service.dart';
 import 'service_ref.dart';
 
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     }
     return super.name;
   }
 
   String get url {
     if (ref == null) {
       return super.url;
     }
     if (pos >= 0) {
       if (ref.loaded) {
-        // Script is loaded, get the line number.
-        Script script = ref;
         return '${super.url}---pos=${pos}';
       } else {
         ref.load().then(_updateProperties);
       }
     }
     return super.url;
   }
 
   ScriptRefElement.created() : super.created();
 }