MediaFormat: added subtitle format

Added KEY_LANGUAGE that for now only refers to subtitles.
Added createSubtitleFormat() method to create base format.

Signed-off-by: Lajos Molnar <lajos@google.com>
Change-Id: I344c36a3fd0d88c285cdebf3f67e549553b37a8e
Bug: 10326117
2 files changed