Use JoinableTaskFactory to call UpdateSearchHost

Avoid using RxApp.MainThreadScheduler.

Author: jcansdale

src/GitHub.VisualStudio/UI/GitHubPane.cs

@@ -56,14 +56,26 @@ public FrameworkElement View
                         return pane?.WhenAnyValue(p => p.IsSearchEnabled, p => p.SearchQuery)
                             ?? Observable.Return(Tuple.Create<bool, string>(false, null));
                     })
-                    .ObserveOn(RxApp.MainThreadScheduler)
-                    .Subscribe(x => UpdateSearchHost(x.Item1, x.Item2));
+                    .Subscribe(x => JoinableTaskFactory.Run(async () =>
+                    {
+                        await JoinableTaskFactory.SwitchToMainThreadAsync();
+                        UpdateSearchHost(x.Item1, x.Item2);
+                    }));
             }
         }
 
-        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
-        public GitHubPane() : base(null)
+        public GitHubPane() : this(ThreadHelper.JoinableTaskContext)
+        {
+        }
+
+        [SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
+        public GitHubPane(JoinableTaskContext joinableTaskContext)
         {
+            joinableTaskContext = joinableTaskContext ?? new JoinableTaskContext();
+            JoinableTaskCollection = joinableTaskContext.CreateCollection();
+            JoinableTaskCollection.DisplayName = nameof(GitHubPane);
+            JoinableTaskFactory = joinableTaskContext.CreateFactory(JoinableTaskCollection);
+
             Caption = "GitHub";
             Content = contentPresenter = new ContentPresenter();
 
@@ -213,5 +225,7 @@ public SearchQuery(string query)
 
             public uint GetTokens(uint dwMaxTokens, IVsSearchToken[] rgpSearchTokens) => 0;
         }
-    }
+
+        public JoinableTaskCollection JoinableTaskCollection { get; }
+        JoinableTaskFactory JoinableTaskFactory { get; }    }
 }