henrik.lundin 9a410dd082 Change NetEq::GetPlayoutTimestamp to return an rtc::Optional<uint32_t>
This is in preparation for changes to when the playout timestamp is
valid.

BUG=webrtc:5669

Review URL: https://codereview.webrtc.org/1853183002

Cr-Commit-Position: refs/heads/master@{#12256}
2016-04-06 08:39:30 +00:00
..
2015-09-29 22:45:23 +00:00
2016-03-08 12:11:00 +00:00
2016-01-13 00:26:55 +00:00
2016-01-13 00:26:55 +00:00