Add TaskPriority as a parameter to SequencedWorkerPool in preparation for TaskScheduler experiment.

ash/sysui/sysui_application.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/sysui/sysui_application.h"
 
 #include <map>
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 186 matching lines @@
     return native_widget;
   }
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetFactory);
 };
 
 }  // namespace
 
 class AshInit {
  public:
-  AshInit() : worker_pool_(new base::SequencedWorkerPool(2, "AshWorkerPool")) {
+  AshInit()
+      : worker_pool_(
+            new base::SequencedWorkerPool(2,
+                                          "AshWorkerPool",
+                                          base::TaskPriority::USER_BLOCKING)) {
     ui::RegisterPathProvider();
   }
 
   ~AshInit() { worker_pool_->Shutdown(); }
 
   aura::Window* root() { return Shell::GetPrimaryRootWindow(); }
 
   void Initialize(::shell::Connector* connector,
                   const ::shell::Identity& identity) {
     InitializeResourceBundle(connector);
@@ skipping 113 matching lines @@
                               mojom::WallpaperControllerRequest request) {
   mojom::WallpaperController* wallpaper_controller =
       static_cast<UserWallpaperDelegateMus*>(
           Shell::GetInstance()->user_wallpaper_delegate());
   wallpaper_controller_bindings_.AddBinding(wallpaper_controller,
                                             std::move(request));
 }
 
 }  // namespace sysui
 }  // namespace ash