TaskScheduler: Set the IO allowed bit in TaskTracker::RunTask().

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 d06a84dc1f47dd7a4cb16f4463a4fa0c486a6dca..50ff5cd8d987c818595e8c179bd2b13dc812049b 100644
--- a/base/task_scheduler/task_tracker.cc
+++ b/base/task_scheduler/task_tracker.cc
@@ -220,11 +220,12 @@ bool TaskTracker::RunTask(std::unique_ptr<Task> task,
 
   if (can_run_task) {
     // All tasks run through here and the scheduler itself doesn't use
-    // singletons. Therefore, it isn't necessary to reset the singleton allowed
-    // bit after running the task.
+    // singletons or file I/O. Therefore, it isn't necessary to reset the
+    // singleton allowed or file I/O allowed bits after running the task.
     ThreadRestrictions::SetSingletonAllowed(
         task->traits.shutdown_behavior() !=
         TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN);
+    ThreadRestrictions::SetIOAllowed(task->traits.with_file_io());
 
     {
       // Set up SequenceToken as expected for the scope of the task.