Make the IsLowPriority API take a cancellation token as well.

src/Features/Core/SolutionCrawler/IWorkCoordinatorPriorityService.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Host;
 
@@ -16,6 +13,6 @@ internal interface IWorkCoordinatorPriorityService : ILanguageService
         /// contained in, and should have work scheduled for it happen after all other documents
         /// in the project.
         /// </summary>
-        Task<bool> IsLowPriorityAsync(Document document);
+        Task<bool> IsLowPriorityAsync(Document document, CancellationToken cancellationToken);
     }
 }

src/Features/Core/SolutionCrawler/WorkCoordinator.SemanticChangeProcessor.cs

@@ -363,7 +363,7 @@ public async Task EnqueueWorkItemAsync(Document document)
 
                         // call to this method is serialized. and only this method does the writing.
                         var priorityService = document.GetLanguageService<IWorkCoordinatorPriorityService>();
-                        var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document).ConfigureAwait(false);
+                        var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document, this.CancellationToken).ConfigureAwait(false);
 
                         _processor.Enqueue(
                             new WorkItem(document.Id, document.Project.Language, InvocationReasons.SemanticChanged,

src/Features/Core/SolutionCrawler/WorkCoordinator.cs

@@ -6,7 +6,6 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Internal.Log;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
@@ -397,7 +396,7 @@ private async Task EnqueueWorkItemAsync(Document document, InvocationReasons inv
                 _shutdownToken.ThrowIfCancellationRequested();
 
                 var priorityService = document.GetLanguageService<IWorkCoordinatorPriorityService>();
-                var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document).ConfigureAwait(false);
+                var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document, _shutdownToken).ConfigureAwait(false);
 
                 var currentMember = GetSyntaxPath(changedMember);
 
@@ -448,7 +447,7 @@ private async Task EnqueueWorkItemAsync(IIncrementalAnalyzer analyzer, IEnumerab
                     }
 
                     var priorityService = document.GetLanguageService<IWorkCoordinatorPriorityService>();
-                    var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document).ConfigureAwait(false);
+                    var isLowPriority = priorityService != null && await priorityService.IsLowPriorityAsync(document, _shutdownToken).ConfigureAwait(false);
 
                     _documentAndProjectWorkerProcessor.Enqueue(
                         new WorkItem(documentId, document.Project.Language, InvocationReasons.Reanalyze,