Add STATUS_UNPLUGGED to RemovableStorageDevice::Status

Author: jp-pino

protobuf_definitions/message_formats.proto

@@ -657,8 +657,9 @@ message RemovableStorageDevice {
   enum Status {
     STATUS_UNSPECIFIED = 0; // Unspecified.
     STATUS_READY = 1; // The storage device is valid and ready for use.
-    STATUS_FORMATTING = 2; // The storage device is being formatted
+    STATUS_FORMATTING = 2; // The storage device is being formatted.
     STATUS_ERROR = 3; // The storage device is in an error state.
+    STATUS_UNPLUGGED = 4; // The storage device is not present.
   }
   string vendor_name = 1; // USB vendor name.
   string model_name = 2; // Model name of the USB storage device.