Do not inherit TaskPriority in TaskTraits.

base/task_scheduler/test_utils.cc

Index: base/task_scheduler/test_utils.cc
diff --git a/base/task_scheduler/test_utils.cc b/base/task_scheduler/test_utils.cc
new file mode 100644
index 0000000000000000000000000000000000000000..fa1dded5dfd6c3a502ba89b1878414f1cb6185a5
--- /dev/null
+++ b/base/task_scheduler/test_utils.cc
@@ -0,0 +1,17 @@
+// Copyright 2017 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 "base/task_scheduler/test_utils.h"
+
+namespace base {
+namespace internal {
+namespace test {
+
+TaskTraits CreateTaskTraits() {
+  return TaskTraits().WithPriority(TaskPriority::USER_VISIBLE);
+}
+
+}  // namespace test
+}  // namespace internal
+}  // namespace base