My best guess at the moment is there's a surface invariants violation in WindowPortMus somewhere. cc'ing some folks. I'll dig more into this next week (I'm OOO for a week).

This isn't really actionable and really turns a momentary glitch into a crash. I think we should convert these into UMA. Passing along to mohsen@ to convert this into a UMA. 

The ideal situation is a user files a repro-able bug with the glitch.

This is a release blocker. I'll assign to myself.

We already report surface invariants violations service-side, so I'm just going to convert the checks into DCHECKs.

I'd also like to merge this back into M69 for reporting purposes:

https://chromium-review.googlesource.com/c/chromium/src/+/1155471

Fady, if this is only for the ksv no need to backport as we're turning it off for 69. Plan is to enable everywhere in 70.

I think killing the client if it abuses surfaces is a bit draconian. I'm going to go ahead with the backport in case there are bugs in other clients.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/96dfe14093fb89c65d68e78b66ea381398592199

commit 96dfe14093fb89c65d68e78b66ea381398592199
Author: Fady Samuel <fsamuel@chromium.org>
Date: Mon Aug 20 21:11:15 2018

Surface Synchronization: Convert invariants violations to DCHECKs

This CL converts some not so useful CHECKs in AsyncLayerTreeFrameSink
into DCHECKs that can be caught in debug builds by developers.

We would like to merge this CL into M69 as well to eliminate a source
of renderer crashes.

Bug:  871450 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I235d068ea72774b020ba7a241507d0f4201d8dc0
Reviewed-on: https://chromium-review.googlesource.com/1181766
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584560}
[modify] https://crrev.com/96dfe14093fb89c65d68e78b66ea381398592199/cc/mojo_embedder/async_layer_tree_frame_sink.cc

So far there aren't any crashes on 70.0.3529.0 which is been released 10 hours back. 

Please find the crash impact on Chrome version here : https://goto.google.com/dbtvq

This bug requires manual review: We are only 13 days from stable.
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), kariahda@(iOS), cindyb@(ChromeOS), govind@(Desktop)

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

This is a very very low risk change. This is changing some CHECKs to DCHECKs.

Approving merge to M69 branch 3497 based on comment #10, #13 and per offline char with fseb@. Pls merge now. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c9994bdf8ae85684694c72f3462c6436237fe452

commit c9994bdf8ae85684694c72f3462c6436237fe452
Author: Fady Samuel <fsamuel@chromium.org>
Date: Tue Aug 21 17:38:23 2018

Surface Synchronization: Convert invariants violations to DCHECKs

This CL converts some not so useful CHECKs in AsyncLayerTreeFrameSink
into DCHECKs that can be caught in debug builds by developers.

We would like to merge this CL into M69 as well to eliminate a source
of renderer crashes.

Bug:  871450 
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I235d068ea72774b020ba7a241507d0f4201d8dc0
Reviewed-on: https://chromium-review.googlesource.com/1181766
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Fady Samuel <fsamuel@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#584560}(cherry picked from commit 96dfe14093fb89c65d68e78b66ea381398592199)
Reviewed-on: https://chromium-review.googlesource.com/1183921
Reviewed-by: Fady Samuel <fsamuel@chromium.org>
Cr-Commit-Position: refs/branch-heads/3497@{#742}
Cr-Branched-From: 271eaf50594eb818c9295dc78d364aea18c82ea8-refs/heads/master@{#576753}
[modify] https://crrev.com/c9994bdf8ae85684694c72f3462c6436237fe452/cc/mojo_embedder/async_layer_tree_frame_sink.cc

M69 Stable promotion is coming VERY soon. Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and request a merge into the release branch ASAP. Merge has to happen latest by 4:00 PM PT Friday (08/24/18) in order to make it to next week stable cut. Thank you.