Refactor RTPPacketHistory to use a packet struct.

Refactor RTPPacketHistory to use a packet struct.

Collects packet information within a struct instead of spreading it out
over different vectors. Adds a fixed-size buffer to the stored packet
instead of using vectors.

BUG=
R=stefan@webrtc.org

Committed: https://crrev.com/c32d2db69bc94480ecb312268c6e6769d4a1cac6
Cr-Commit-Position: refs/heads/master@{#9926}

[pbos-webrtc, 2015-09-11 13:38:01]

PTAL woo

[pbos-webrtc, 2015-09-11 13:49:14]

remove max packet size as a parameter

[stefan-webrtc, 2015-09-11 13:51:11]

lgtm

[pbos-webrtc, 2015-09-11 13:52:18]

The CQ bit was checked by pbos@webrtc.org

[commit-bot: I haz the power, 2015-09-11 13:52:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1340573002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1340573002/20001

[commit-bot: I haz the power, 2015-09-11 15:33:41]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-09-11 15:33:53]

Patchset 2 (id:??) landed as
https://crrev.com/c32d2db69bc94480ecb312268c6e6769d4a1cac6
Cr-Commit-Position: refs/heads/master@{#9926}