Before this change, the player state would be STATE_ENDED then
STATE_BUFFERING (when the postroll ad was marked as played) then
STATE_ENDED again.
Queueing a final content media period with start point equal to
the content duration after a postroll ensures that the player
state doesn't change to STATE_ENDED transiently.
Switch from using C.TIME_END_OF_SOURCE to C.TIME_UNSET for media
periods that should not have an end point and are not followed
by an ad.
Content media periods before postrolls have end position
C.TIME_END_OF_SOURCE. If the postroll ad loads, its content
position is set to the content duration, which should be known
at the point of loading the postroll, then a final 'empty'
content media period with start position equal to its duration
is queued. If the postroll fails to load, this empty content
media period is queued up directly after the preceding content
media period.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=219443683
1094da2b61