Start getting tests running

src/EditorFeatures/Core/Shared/Utilities/ForegroundThreadAffinitizedObject.cs

@@ -14,10 +14,7 @@ namespace Microsoft.CodeAnalysis.Editor.Shared.Utilities
     /// </summary>
     internal class ForegroundThreadAffinitizedObject
     {
-        [ThreadStatic]
         private static Thread s_foregroundThread;
-
-        [ThreadStatic]
         private static TaskScheduler s_foregroundTaskScheduler;
 
         internal static Thread ForegroundThread

src/EditorFeatures/TestUtilities/Async/WaitHelper.cs

@@ -13,8 +13,7 @@ public static class WaitHelper
     {
         public static void WaitForDispatchedOperationsToComplete(DispatcherPriority priority)
         {
-            Action action = delegate { };
-            new FrameworkElement().Dispatcher.Invoke(action, priority);
+            new FrameworkElement().Dispatcher.DoEvents();
         }
 
         public static void PumpingWait(this Task task)

src/EditorFeatures/TestUtilities/DispatcherExtensions.cs

@@ -18,7 +18,7 @@ public static void DoEvents(this Dispatcher dispatcher)
             // complete mark the frame as complete so the dispatcher loop
             // pops out (stops).
             var operation = dispatcher.BeginInvoke(
-                DispatcherPriority.Background, callback, frame);
+                DispatcherPriority.SystemIdle, callback, frame);
 
             // Start the loop.  It will process all items in the queue, then 
             // will process the above callback.  That callback will tell the