Miscellaneous Observatory UI improvements

runtime/bin/vmservice/client/lib/src/app/view_model.dart

Index: runtime/bin/vmservice/client/lib/src/app/view_model.dart
diff --git a/runtime/bin/vmservice/client/lib/src/app/view_model.dart b/runtime/bin/vmservice/client/lib/src/app/view_model.dart
index dda6c81ab8dc743269607d1fd861e3d40d6e691b..3be79ea94e132ec56432d3507b0c120f989831bc 100644
--- a/runtime/bin/vmservice/client/lib/src/app/view_model.dart
+++ b/runtime/bin/vmservice/client/lib/src/app/view_model.dart
@@ -9,6 +9,11 @@ abstract class TableTreeRow extends Observable {
   @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,
@@ -22,8 +27,10 @@ abstract class TableTreeRow extends Observable {
     if (changed) {
       // If the state has changed, fire callbacks.
       if (_expanded) {
+        expander = arrowDownRight;
         onShow();
       } else {
+        expander = arrowRight;
         onHide();
       }
     }