Do not inherit TaskPriority in TaskTraits.

base/task_scheduler/task_tracker.cc

Index: base/task_scheduler/task_tracker.cc
diff --git a/base/task_scheduler/task_tracker.cc b/base/task_scheduler/task_tracker.cc
index da21d5ea8ef510c33636cc993b34e3501aa09101..81e6669bdae6f3b5dc9e980618b973883725480b 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -219,6 +219,8 @@ void TaskTracker::Flush() {
 
 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;
@@ -235,6 +237,8 @@ bool TaskTracker::WillPostTask(const Task* task) {
 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 =