Do not inherit TaskPriority in TaskTraits.

base/task_scheduler/task_tracker.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 "base/task_scheduler/task_tracker.h"
 
 #include <limits>
 #include <string>
 
 #include "base/callback.h"
@@ skipping 201 matching lines @@
 void TaskTracker::Flush() {
   AutoSchedulerLock auto_lock(flush_lock_);
   while (subtle::NoBarrier_Load(&num_pending_undelayed_tasks_) != 0 &&
          !IsShutdownComplete()) {
     flush_cv_->Wait();
   }
 }
 
 bool TaskTracker::WillPostTask(const Task* task) {
   DCHECK(task);
+  DCHECK_LE(static_cast<int>(task->traits.priority()),
+            static_cast<int>(TaskPriority::HIGHEST));
 
   if (!BeforePostTask(task->traits.shutdown_behavior()))
     return false;
 
   if (task->delayed_run_time.is_null())
     subtle::NoBarrier_AtomicIncrement(&num_pending_undelayed_tasks_, 1);
 
   debug::TaskAnnotator task_annotator;
   task_annotator.DidQueueTask(kQueueFunctionName, *task);
 
   return true;
 }
 
 bool TaskTracker::RunTask(std::unique_ptr<Task> task,
                           const SequenceToken& sequence_token) {
   DCHECK(task);
+  DCHECK_LE(static_cast<int>(task->traits.priority()),
+            static_cast<int>(TaskPriority::HIGHEST));
   DCHECK(sequence_token.IsValid());
 
   const TaskShutdownBehavior shutdown_behavior =
       task->traits.shutdown_behavior();
   const bool can_run_task = BeforeRunTask(shutdown_behavior);
   const bool is_delayed = !task->delayed_run_time.is_null();
 
   if (can_run_task) {
     RecordTaskLatencyHistogram(task.get());
 
@@ skipping 245 matching lines @@
   task_latency_histograms_[static_cast<int>(task->traits.priority())]
                           [task->traits.may_block() ||
                                    task->traits.with_base_sync_primitives()
                                ? 1
                                : 0]
                               ->AddTime(task_latency);
 }
 
 }  // namespace internal
 }  // namespace base