Switch to using SourceLocation universally in service protocol.

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';
 
@@ skipping 45 matching lines @@
         return '${super.url}---pos=${pos}';
       } else {
         ref.load().then(_updateProperties);
       }
     }
     return super.url;
   }
 
   ScriptRefElement.created() : super.created();
 }
+
+@CustomTag('source-link')
+class SourceLinkElement extends PolymerElement {
+  SourceLinkElement.created() : super.created();
+
+  @published SourceLocation location;
+}