Fix assertion starting cast_shell (breaking thread IO restrictions).

ui/events/ozone/device/device_manager_manual.cc

Index: ui/events/ozone/device/device_manager_manual.cc
diff --git a/ui/events/ozone/device/device_manager_manual.cc b/ui/events/ozone/device/device_manager_manual.cc
index c86ffccf62bdae50079e2927d77841a24cefdc7d..059fbe7494714e4665156ab84127338776de2531 100644
--- a/ui/events/ozone/device/device_manager_manual.cc
+++ b/ui/events/ozone/device/device_manager_manual.cc
@@ -5,6 +5,7 @@
 #include "ui/events/ozone/device/device_manager_manual.h"
 
 #include "base/files/file_enumerator.h"
+#include "base/threading/thread_restrictions.h"
 #include "ui/events/ozone/device/device_event.h"
 #include "ui/events/ozone/device/device_event_observer.h"
 
@@ -15,6 +16,7 @@ DeviceManagerManual::DeviceManagerManual() {}
 DeviceManagerManual::~DeviceManagerManual() {}
 
 void DeviceManagerManual::ScanDevices(DeviceEventObserver* observer) {
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   base::FileEnumerator file_enum(base::FilePath("/dev/input"),
                                  false,
                                  base::FileEnumerator::FILES,