Enable automatic resizing for RTX-enabled senders.

Enable automatic resizing for RTX-enabled senders.

These were accidentally disabled due to checking ssrcs_.size() (which
includes RTX SSRCs) instead of rtp.ssrcs.size() to determine whether a
stream is simulcast or not.

BUG=webrtc:4965
R=asapersson@webrtc.org

Committed: https://chromium.googlesource.com/external/webrtc/+/2feafdb742226f57588d9c95bc25b2202166688f

[pbos-webrtc, 2015-09-09 11:58:58]

The CQ bit was checked by pbos@webrtc.org

[pbos-webrtc, 2015-09-09 11:59:05]

Oops, PTAL. :|

[commit-bot: I haz the power, 2015-09-09 11:59:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318193003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318193003/1

[commit-bot: I haz the power, 2015-09-09 11:59:14]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-09 11:59:15]

No L-G-T-M from a valid reviewer yet. Only full committers are accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[pbos-webrtc, 2015-09-09 12:00:14]

The CQ bit was checked by pbos@webrtc.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-09 12:00:20]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318193003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318193003/1

[pbos-webrtc, 2015-09-09 12:01:17]

fix typo

[åsapersson, 2015-09-09 12:13:21]

lgtm

[pbos-webrtc, 2015-09-09 12:32:35]

Committed patchset #2 (id:20001) manually as
2feafdb742226f57588d9c95bc25b2202166688f (presubmit successful).