Merge WebRTC r18998 and r19018 to M60 branch

Merge WebRTC r18998 and r19018 to M60 branch

This CL is cherry pick of the following two commits:

1) RtpFrameReferenceFinder VP8 reference calculation fix.

Review-Url: https://codereview.webrtc.org/2980943003
Cr-Commit-Position: refs/heads/master@{#19018}

2) Fix potential incorrect sync flags used with screenshare TL stream.

Review-Url: https://codereview.webrtc.org/2978743002
Cr-Commit-Position: refs/heads/master@{#18999}

TEST=webrtc unit tests plus manual verification.
BUG=chromium:748417, webrtc:7768, webrtc:7980
R=philipel@webrtc.org

Review-Url: https://codereview.webrtc.org/2992123002 .
Cr-Commit-Position: refs/branch-heads/60@{#11}
Cr-Branched-From: c61bf947b4ac31f3500858ffcae6fee39d799930-refs/heads/master@{#18252}
Committed: https://chromium.googlesource.com/external/webrtc/+/6294a7eb71c891e9ea41273a7a94113f6802d0da

[sprang_webrtc, 2017-08-01 08:17:43]

sprang@webrtc.org changed reviewers:
+ philipel@webrtc.org

[philipel, 2017-08-01 08:19:17]

lgtm

[sprang_webrtc, 2017-08-01 09:33:43]

Description was changed from

==========
Merge WebRTC r18998 and r19018 to M60 branch

This CL is cherry pick of the following two commits:


1) RtpFrameReferenceFinder VP8 reference calculation fix.

Review-Url: https://codereview.webrtc.org/2980943003
Cr-Commit-Position: refs/heads/master@{#19018}


2) Fix potential incorrect sync flags used with screenshare TL stream.

Review-Url: https://codereview.webrtc.org/2978743002
Cr-Commit-Position: refs/heads/master@{#18999}


TEST=webrtc unit tests plus manual verification.
BUG=chromium:748417, webrtc:7768, webrtc:7980
==========

to

==========
Merge WebRTC r18998 and r19018 to M60 branch

This CL is cherry pick of the following two commits:

1) RtpFrameReferenceFinder VP8 reference calculation fix.

Review-Url: https://codereview.webrtc.org/2980943003
Cr-Commit-Position: refs/heads/master@{#19018}

2) Fix potential incorrect sync flags used with screenshare TL stream.

Review-Url: https://codereview.webrtc.org/2978743002
Cr-Commit-Position: refs/heads/master@{#18999}

TEST=webrtc unit tests plus manual verification.
BUG=chromium:748417, webrtc:7768, webrtc:7980
R=philipel@webrtc.org

Review-Url: https://codereview.webrtc.org/2992123002 .
Cr-Commit-Position: refs/branch-heads/60@{#11}
Cr-Branched-From:
c61bf947b4ac31f3500858ffcae6fee39d799930-refs/heads/master@{#18252}
Committed:
https://chromium.googlesource.com/external/webrtc/+/6294a7eb71c891e9ea41273a7...
==========

[sprang_webrtc, 2017-08-01 09:33:45]

Committed patchset #1 (id:1) manually as
6294a7eb71c891e9ea41273a7a94113f6802d0da.