Yuri can we please list the test cases here in more detail, particularly cases wrt security, and protected media playback

1. I don't believe this is asking for security reasons.

2. Protected media playback is interesting: We *do* want to confirm media playback falls-back to the non-protected surface impl when tab capture is active (as discussed with other stakeholders). So, we should see about testing for that.

3. The original purpose is just to make sure Surface aggregation works and results in the full tab (and all nested Surfaces) being captured as one composited unit.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/13eae2005d7b585f1cf3b9911aa797c1dd4e3862

commit 13eae2005d7b585f1cf3b9911aa797c1dd4e3862
Author: Yuri Wiitala <miu@chromium.org>
Date: Wed Feb 28 12:57:13 2018

Add cross-site tab capture test, and fix an OnFrameDamaged() assumption.

Adds a browser test to confirm that tab capture grabs all content and
content updates when cross-site render process isolation is turned on.

The addition of this test revealed a pre-existing bug where the consumer
would not get a video frame for updated content. This happened whenever
OnFrameDamaged() was being called before OnBeginFrame() (which can
happen when Surfaces are changed).

Bug:  808718 
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_mojo
Change-Id: Ic965ece20d4c40eb65cdb78452148283935e5184
Reviewed-on: https://chromium-review.googlesource.com/936661
Reviewed-by: Xiangjun Zhang <xjz@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539806}
[modify] https://crrev.com/13eae2005d7b585f1cf3b9911aa797c1dd4e3862/components/viz/service/frame_sinks/video_capture/frame_sink_video_capturer_impl.cc
[modify] https://crrev.com/13eae2005d7b585f1cf3b9911aa797c1dd4e3862/content/browser/media/capture/web_contents_video_capture_device_browsertest.cc

Since writing the test revealed a bug (that was fixed), requesting merge.

This bug requires manual review: We don't branch M66 until 2018-03-01.
Please contact the milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), josafat@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Oh, M-66 hasn't branched yet. Silly me!