Looks like this issue is affecting M50 as well.  Adding ReleaseBlock as this is causing lots of video freezing for user in certain circumstances.  We should merge after confirming the fix in tomorrow's canary.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/411ea14c10f64b67a25985619583a5331e724d57

commit 411ea14c10f64b67a25985619583a5331e724d57
Author: xjz <xjz@chromium.org>
Date: Mon Apr 04 23:21:39 2016

Reset NACK/ACK list when parsing a new RTCP packet.
The NACK/ACK frames/packets list need to be reset before parsing each
RTCP packet as the parser is shared by all RTCP packets on sender side.
This caused the performance regression and potentially video freezing
as well.

BUG= 600527 

Review URL: https://codereview.chromium.org/1853253003

Cr-Commit-Position: refs/heads/master@{#385046}

[modify] https://crrev.com/411ea14c10f64b67a25985619583a5331e724d57/media/cast/net/rtcp/rtcp_utility.cc

Requesting merge for M50.  This resolves an issue where we are re-transmitting the same packets, eating up the user's local WiFi bandwidth.

Your change meets the bar and is auto-approved for M50 (branch: 2661)

Please merge your change to M50 branch 2661 by 5:00 PM PST on April 8th,Friday to make into the desktop Stable final build cut. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e877754f597c1c2fa8ff411be0c2c6ade0cd6c9f

commit e877754f597c1c2fa8ff411be0c2c6ade0cd6c9f
Author: Yuri Wiitala <miu@chromium.org>
Date: Thu Apr 07 19:16:48 2016

Reset NACK/ACK list when parsing a new RTCP packet. The NACK/ACK frames/packets list need to be reset before parsing each RTCP packet as the parser is shared by all RTCP packets on sender side. This caused the performance regression and potentially video freezing as well.

BUG= 600527 

Review URL: https://codereview.chromium.org/1853253003

Cr-Commit-Position: refs/heads/master@{#385046}
(cherry picked from commit 411ea14c10f64b67a25985619583a5331e724d57)

Review URL: https://codereview.chromium.org/1875433002 .

Cr-Commit-Position: refs/branch-heads/2661@{#510}
Cr-Branched-From: ef6f6ae5e4c96622286b563658d5cd62a6cf1197-refs/heads/master@{#378081}

[modify] https://crrev.com/e877754f597c1c2fa8ff411be0c2c6ade0cd6c9f/media/cast/net/rtcp/rtcp_utility.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bcbfee418884ef234f36d8897254dd7739716880

commit bcbfee418884ef234f36d8897254dd7739716880
Author: miu <miu@chromium.org>
Date: Thu Apr 07 20:45:38 2016

Revert of Reset NACK/ACK list when parsing a new RTCP packet. The NACK/ACK frames/packets list need to be res… (patchset #1 id:1 of https://codereview.chromium.org/1875433002/ )

Reason for revert:
This change needs to be slightly modified since M50 does not have the |received_later_frames| set.

Original issue's description:
> Reset NACK/ACK list when parsing a new RTCP packet. The NACK/ACK frames/packets list need to be reset before parsing each RTCP packet as the parser is shared by all RTCP packets on sender side. This caused the performance regression and potentially video freezing as well.
>
> BUG= 600527 
>
> Review URL: https://codereview.chromium.org/1853253003
>
> Cr-Commit-Position: refs/heads/master@{#385046}
> (cherry picked from commit 411ea14c10f64b67a25985619583a5331e724d57)
>
> Committed: https://chromium.googlesource.com/chromium/src/+/e877754f597c1c2fa8ff411be0c2c6ade0cd6c9f

TBR=xjz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 600527 

Review URL: https://codereview.chromium.org/1869163002

Cr-Commit-Position: refs/branch-heads/2661@{#512}
Cr-Branched-From: ef6f6ae5e4c96622286b563658d5cd62a6cf1197-refs/heads/master@{#378081}

[modify] https://crrev.com/bcbfee418884ef234f36d8897254dd7739716880/media/cast/net/rtcp/rtcp_utility.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f380e7c6b79c8dfcda31cf7efdfd27b6a2575283

commit f380e7c6b79c8dfcda31cf7efdfd27b6a2575283
Author: miu <miu@chromium.org>
Date: Thu Apr 07 21:38:16 2016

Re-land (rebased for M50): Reset NACK/ACK list when parsing a new RTCP packet.

The NACK/ACK frames/packets list need to be reset before parsing each RTCP packet as the parser is shared by all RTCP packets on sender side. This caused the performance regression and potentially video freezing as well.

TBR=xjz@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG= 600527 

Review URL: https://codereview.chromium.org/1853253003

Cr-Commit-Position: refs/heads/master@{#385046}
(cherry picked from commit 411ea14c10f64b67a25985619583a5331e724d57)

Review URL: https://codereview.chromium.org/1867883003

Cr-Commit-Position: refs/branch-heads/2661@{#513}
Cr-Branched-From: ef6f6ae5e4c96622286b563658d5cd62a6cf1197-refs/heads/master@{#378081}

[modify] https://crrev.com/f380e7c6b79c8dfcda31cf7efdfd27b6a2575283/media/cast/net/rtcp/rtcp_utility.cc