Reland of Initialize/configure video encoders asychronously.

Reland of Initialize/configure video encoders asychronously. (patchset #1 id:1 of https://codereview.webrtc.org/1821983002/ )

Reason for revert:
RTCVideoEncoder has been updated to not make assumptions on calling threads/post back to a worker thread. This should now be landable again.

Original issue's description:
> Revert of Initialize/configure video encoders asychronously. (patchset #4 id:60001 of https://codereview.webrtc.org/1757313002/ )
>
> Reason for revert:
> Breaks RTCVideoEncoder which has incorrect assumptions on where InitEncode etc. is called from. Temporarily reverting until RTCVideoEncoder has been updated.
>
> Original issue's description:
> > Initialize/configure video encoders asychronously.
> >
> > Greatly speeds up setRemoteDescription() by moving encoder initialization
> > off the main worker thread, which is free to move onto gathering ICE
> > candidates and other tasks while InitEncode() is performed. It also
> > un-blocks PeerConnection GetStats() which is no longer blocked on
> > encoder initialization.
> >
> > BUG=webrtc:5410
> > R=stefan@webrtc.org
> >
> > Committed: https://chromium.googlesource.com/external/webrtc/+/fb647a67be94bb3c940d8b5fba01972f7ce91a29
>
> R=stefan@webrtc.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=chromium:595274, chromium:595308, webrtc:5410
>
> Committed: https://crrev.com/81cbd924447d507559dbd6e6d1f9fe439fcf2716
> Cr-Commit-Position: refs/heads/master@{#12086}

TBR=stefan@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:595274, chromium:595308, webrtc:5410
Committed: https://crrev.com/14fe708f3d6357a3e3f9b62d8a6a9e310af86fcd
Cr-Commit-Position: refs/heads/master@{#12446}

[pbos-webrtc, 2016-04-20 09:45:30]

Created Reland of Initialize/configure video encoders asychronously.

[pbos-webrtc, 2016-04-20 10:13:07]

rebase

[pbos-webrtc, 2016-04-20 10:14:38]

The CQ bit was checked by pbos@webrtc.org

[commit-bot: I haz the power, 2016-04-20 10:14:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1896413002/130001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1896413002/130001

[pbos-webrtc, 2016-04-20 10:20:12]

+cc perkj@,nisse@: This is the CL that'll let us post video frames from a
non-worker thread.

[pbos-webrtc, 2016-04-20 10:20:17]

The CQ bit was unchecked by pbos@webrtc.org

[pbos-webrtc, 2016-04-20 10:20:29]

On 2016/04/20 10:20:12, pbos-webrtc wrote:
> +cc perkj@,nisse@: This is the CL that'll let us post video frames from a
> non-worker thread.

To be landed pending https://codereview.chromium.org/1845563006/.

[pbos-webrtc, 2016-04-20 12:34:10]

The CQ bit was checked by pbos@webrtc.org

[commit-bot: I haz the power, 2016-04-20 12:34:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1896413002/130001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1896413002/130001

[pbos-webrtc, 2016-04-20 12:34:15]

The CQ bit was unchecked by pbos@webrtc.org

[pbos-webrtc, 2016-04-20 12:34:27]

rebase2

[pbos-webrtc, 2016-04-20 12:34:37]

The CQ bit was checked by pbos@webrtc.org

[commit-bot: I haz the power, 2016-04-20 12:34:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1896413002/150001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1896413002/150001

[commit-bot: I haz the power, 2016-04-20 13:36:00]

Committed patchset #3 (id:150001)

[commit-bot: I haz the power, 2016-04-20 13:58:03]

Description was changed from

==========
Reland of Initialize/configure video encoders asychronously. (patchset #1 id:1
of https://codereview.webrtc.org/1821983002/ )

Reason for revert:
RTCVideoEncoder has been updated to not make assumptions on calling threads/post
back to a worker thread. This should now be landable again.

Original issue's description:
> Revert of Initialize/configure video encoders asychronously. (patchset #4
id:60001 of https://codereview.webrtc.org/1757313002/ )
> 
> Reason for revert:
> Breaks RTCVideoEncoder which has incorrect assumptions on where InitEncode
etc. is called from. Temporarily reverting until RTCVideoEncoder has been
updated.
> 
> Original issue's description:
> > Initialize/configure video encoders asychronously.
> >
> > Greatly speeds up setRemoteDescription() by moving encoder initialization
> > off the main worker thread, which is free to move onto gathering ICE
> > candidates and other tasks while InitEncode() is performed. It also
> > un-blocks PeerConnection GetStats() which is no longer blocked on
> > encoder initialization.
> >
> > BUG=webrtc:5410
> > R=stefan@webrtc.org
> >
> > Committed:
https://chromium.googlesource.com/external/webrtc/+/fb647a67be94bb3c940d8b5fb...
> 
> R=stefan@webrtc.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=chromium:595274, chromium:595308, webrtc:5410
> 
> Committed: https://crrev.com/81cbd924447d507559dbd6e6d1f9fe439fcf2716
> Cr-Commit-Position: refs/heads/master@{#12086}

TBR=stefan@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:595274, chromium:595308, webrtc:5410
==========

to

==========
Reland of Initialize/configure video encoders asychronously. (patchset #1 id:1
of https://codereview.webrtc.org/1821983002/ )

Reason for revert:
RTCVideoEncoder has been updated to not make assumptions on calling threads/post
back to a worker thread. This should now be landable again.

Original issue's description:
> Revert of Initialize/configure video encoders asychronously. (patchset #4
id:60001 of https://codereview.webrtc.org/1757313002/ )
>
> Reason for revert:
> Breaks RTCVideoEncoder which has incorrect assumptions on where InitEncode
etc. is called from. Temporarily reverting until RTCVideoEncoder has been
updated.
>
> Original issue's description:
> > Initialize/configure video encoders asychronously.
> >
> > Greatly speeds up setRemoteDescription() by moving encoder initialization
> > off the main worker thread, which is free to move onto gathering ICE
> > candidates and other tasks while InitEncode() is performed. It also
> > un-blocks PeerConnection GetStats() which is no longer blocked on
> > encoder initialization.
> >
> > BUG=webrtc:5410
> > R=stefan@webrtc.org
> >
> > Committed:
https://chromium.googlesource.com/external/webrtc/+/fb647a67be94bb3c940d8b5fb...
>
> R=stefan@webrtc.org
> # Not skipping CQ checks because original CL landed more than 1 days ago.
> BUG=chromium:595274, chromium:595308, webrtc:5410
>
> Committed: https://crrev.com/81cbd924447d507559dbd6e6d1f9fe439fcf2716
> Cr-Commit-Position: refs/heads/master@{#12086}

TBR=stefan@webrtc.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:595274, chromium:595308, webrtc:5410

Committed: https://crrev.com/14fe708f3d6357a3e3f9b62d8a6a9e310af86fcd
Cr-Commit-Position: refs/heads/master@{#12446}
==========

[commit-bot: I haz the power, 2016-04-20 13:58:04]

Patchset 3 (id:??) landed as
https://crrev.com/14fe708f3d6357a3e3f9b62d8a6a9e310af86fcd
Cr-Commit-Position: refs/heads/master@{#12446}