Centralized event streams

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

 // Copyright (c) 2016, 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 source_link_element;
 
 import 'dart:html';
 import 'dart:async';
 import 'package:observatory/models.dart'
   show IsolateRef, SourceLocation, Script, ScriptRepository;
@@ skipping 26 matching lines @@
     e._location = location;
     e._repository = repository;
     return e;
   }
 
   SourceLinkElement.created() : super.created();
 
   @override
   void attached() {
     super.attached();
-    assert(location != null);
-    _r.enable();
     _repository.get(_location.script.id).then((script) {
       _script = script;
       _r.dirty();
     });
+    _r.enable();
   }
 
   @override
-  void detached() { super.detached(); children = []; _r.disable(notify: true); }
+  void detached() {
+    super.detached();
+    children = [];
+    _r.disable(notify: true);
+  }
 
   Future render() async {
     if (_script == null) {
       children = [new SpanElement()..text = '<LOADING>'];
     } else {
       String label = _script.uri.split('/').last;
       int token = _location.tokenPos;
       int line = _script.tokenToLine(token);
       int column = _script.tokenToCol(token);
       children = [
         new AnchorElement(
             href: Uris.inspect(isolate, object: _script, pos: token))
           ..title = _script.uri
           ..text = '${label}:${line}:${column}'
       ];
     }
   }
 }