Adjust fire time of a timed text message before firing it.

related-to-bug: 6501328

o When Video/Audio is stuttering, subtitle's firing time should be
adjusted.

Change-Id: I0e7e8a1796cb2b3c8a09c8fbd41690bce2689e85
(cherry picked from gtv: commit b2c3aedcb6c145e33ded39ef81e3202b2419469f)