Use the chrome.system.storage API to query storage device information and be notified when a removable storage device is attached and detached.

class ChromeSystemStorage extends ChromeApi {
 static final JsObject _system_storage = chrome['system']['storage'];

 ChromeSystemStorage._();

 bool get available => _system_storage != null;

 /**
  * Get the storage information from the system. The argument passed to the
  * callback is an array of StorageUnitInfo objects.
  */
 Future<List<StorageUnitInfo>> getInfo() {
   if (_system_storage == null) _throwNotAvailable();

   var completer = new ChromeCompleter<List<StorageUnitInfo>>.oneArg((e) => listify(e, _createStorageUnitInfo));
   _system_storage.callMethod('getInfo', [completer.callback]);
   return completer.future;
 }

 /**
  * Ejects a removable storage device.
  */
 Future<EjectDeviceResultCode> ejectDevice(String id) {
   if (_system_storage == null) _throwNotAvailable();

   var completer = new ChromeCompleter<EjectDeviceResultCode>.oneArg(_createEjectDeviceResultCode);
   _system_storage.callMethod('ejectDevice', [id, completer.callback]);
   return completer.future;
 }

 /**
  * Get the available capacity of a specified [id] storage device. The [id] is
  * the transient device ID from StorageUnitInfo.
  */
 Future<StorageAvailableCapacityInfo> getAvailableCapacity(String id) {
   if (_system_storage == null) _throwNotAvailable();

   var completer = new ChromeCompleter<StorageAvailableCapacityInfo>.oneArg(_createStorageAvailableCapacityInfo);
   _system_storage.callMethod('getAvailableCapacity', [id, completer.callback]);
   return completer.future;
 }

 Stream<StorageUnitInfo> get onAttached => _onAttached.stream;

 final ChromeStreamController<StorageUnitInfo> _onAttached =
     new ChromeStreamController<StorageUnitInfo>.oneArg(_system_storage, 'onAttached', _createStorageUnitInfo);

 Stream<String> get onDetached => _onDetached.stream;

 final ChromeStreamController<String> _onDetached =
     new ChromeStreamController<String>.oneArg(_system_storage, 'onDetached', selfConverter);

 void _throwNotAvailable() {
   throw new UnsupportedError("'chrome.system.storage' is not available");
 }
}