Fix assertion starting cast_shell (breaking thread IO restrictions).

ui/events/ozone/device/device_manager_manual.h

Index: ui/events/ozone/device/device_manager_manual.h
diff --git a/ui/events/ozone/device/device_manager_manual.h b/ui/events/ozone/device/device_manager_manual.h
index 09e9875ba6fcc9758d4b3283d133693803184bdc..d158365d9dc1e0f16a0defa97b09ecf6b6751eac 100644
--- a/ui/events/ozone/device/device_manager_manual.h
+++ b/ui/events/ozone/device/device_manager_manual.h
@@ -5,9 +5,16 @@
 #ifndef UI_EVENTS_OZONE_DEVICE_DEVICE_MANAGER_MANUAL_H_
 #define UI_EVENTS_OZONE_DEVICE_DEVICE_MANAGER_MANUAL_H_
 
+#include <vector>
+
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "ui/events/ozone/device/device_manager.h"
 
+namespace base {
+class FilePath;
+}
+
 namespace ui {
 
 class DeviceManagerManual : public DeviceManager {
@@ -21,6 +28,14 @@ class DeviceManagerManual : public DeviceManager {
   void AddObserver(DeviceEventObserver* observer) override;
   void RemoveObserver(DeviceEventObserver* observer) override;
 
+  void OnDevicesScanned(std::vector<base::FilePath>* result);
+
+  bool have_scanned_devices_;
+  std::vector<base::FilePath> devices_;
+  ObserverList<DeviceEventObserver> observers_;
+
+  base::WeakPtrFactory<DeviceManagerManual> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DeviceManagerManual);
 };