Reland "Add event parameters to MtpEvent."

The CL was previously reviewed at ag/842930.

> We can obtain detailed information of MtpEvent from devices. e.g. object
> handle of changed object.  The CL adds the detailed information as
> properties of MtpEvent class.
>
> BUG=26480986

Change-Id: I93afad9caf118d74cd0923d70242133c4fb2a648