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

services/shell/runner/host/child_process_host_unittest.cc

 // Copyright 2014 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.
 
 // Note: This file also tests child_process.*.
 
 #include "services/shell/runner/host/child_process_host.h"
 
 #include <memory>
 #include <utility>
@@ skipping 60 matching lines @@
 #else
 #define MAYBE_StartJoin StartJoin
 #endif  // defined(OS_ANDROID)
 // Just tests starting the child process and joining it (without starting an
 // app).
 TEST(ChildProcessHostTest, MAYBE_StartJoin) {
   base::FilePath shell_dir;
   PathService::Get(base::DIR_MODULE, &shell_dir);
   base::MessageLoop message_loop;
   scoped_refptr<base::SequencedWorkerPool> blocking_pool(
-      new base::SequencedWorkerPool(3, "blocking_pool"));
+      new base::SequencedWorkerPool(3, "blocking_pool",
+                                    base::TaskPriority::USER_VISIBLE));
 
   base::Thread io_thread("io_thread");
   base::Thread::Options options;
   options.message_loop_type = base::MessageLoop::TYPE_IO;
   io_thread.StartWithOptions(options);
 
   ProcessDelegate delegate;
   mojo::edk::InitIPCSupport(&delegate, io_thread.task_runner());
 
   NativeRunnerDelegateImpl native_runner_delegate;
   ChildProcessHost child_process_host(blocking_pool.get(),
                                       &native_runner_delegate, false,
                                       Identity(), base::FilePath());
   base::RunLoop run_loop;
   child_process_host.Start(
       Identity(),
       base::Bind(&ProcessReadyCallbackAdapater, run_loop.QuitClosure()),
       base::Bind(&base::DoNothing));
   run_loop.Run();
 
   child_process_host.Join();
   blocking_pool->Shutdown();
   mojo::edk::ShutdownIPCSupport();
   EXPECT_EQ(1u, native_runner_delegate.get_and_clear_adjust_count());
 }
 
 }  // namespace
 }  // namespace shell