Miscellaneous Observatory UI improvements

runtime/bin/vmservice/client/lib/src/app/view_model.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.
 
 part of app;
 
 abstract class TableTreeRow extends Observable {
   final TableTreeRow parent;
   @observable final int depth;
   @observable final List<TableTreeRow> children = new List<TableTreeRow>();
   @observable final List<String> columns = [];
+  static const arrowRight = '\u2192';
+  static const arrowDownRight = '\u21b3';
+  // TODO(johnmccutchan): Move expander display decisions into html once
+  // tables and templates are better supported.
+  @observable String expander = arrowRight;
 
   TableTreeRow(TableTreeRow parent) :
       parent = parent,
       depth = parent != null ? parent.depth+1 : 0;
 
   bool _expanded = false;
   bool get expanded => _expanded;
   set expanded(bool expanded) {
     var changed = _expanded != expanded;
     _expanded = expanded;
     if (changed) {
       // If the state has changed, fire callbacks.
       if (_expanded) {
+        expander = arrowDownRight;
         onShow();
       } else {
+        expander = arrowRight;
         onHide();
       }
     }
   }
 
   bool toggle() {
     expanded = !expanded;
     return expanded;
   }
 
@@ skipping 48 matching lines @@
         _collapse(row.children[i]);
       }
     }
     // Collapse this row.
     row.expanded = false;
     // Remove all children.
     int index = _index(row);
     rows.removeRange(index + 1, index + 1 + childCount);
   }
 }