Fetch mime type from file name when format code does not help.

MTP spec defines format code as a file type of object, but we don't have
format code for some file types like PDF. This CL adds fallback that
tries to obtain mime type from file name in such case.

BUG=27004957

Change-Id: Id61352bf4726f4e044e57edadcefbf179fe3f882
2 files changed