Small cleanup to Code and Profiler pages

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';
+  static const showExpanderStyle = 'cursor: pointer;';
+  static const hideExpanderStyle = 'visibility:hidden;';
+
   // TODO(johnmccutchan): Move expander display decisions into html once
   // tables and templates are better supported.
   @observable String expander = arrowRight;
+  @observable String expanderStyle = showExpanderStyle;
 
   TableTreeRow(TableTreeRow parent) :
       parent = parent,
-      depth = parent != null ? parent.depth+1 : 0;
+      depth = parent != null ? parent.depth+1 : 0 {
+    if (!hasChildren()) {
+      expanderStyle = hideExpanderStyle;
+    }
+  }
 
   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;
   }
 
+  bool hasChildren();
+
   /// Fired when the tree row is expanded. Add children rows here.
   void onShow();
 
   /// Fired when the tree row is collapsed.
   void onHide();
 }
 
 class TableTree extends Observable {
   @observable final List<TableTreeRow> rows = toObservable([]);
 
@@ skipping 125 matching lines @@
     if (column != _sortColumnIndex) {
       return columns[column].label + '\u2003';
     }
     return columns[column].label + (_sortDescending ? arrowUp : arrowDown);
   }
 
   @reflectable dynamic getValue(int row, int column) {
     return rows[row].values[column];
   }
 }