For 64-bit, this is the first build with these failures: https://build.chromium.org/p/chromium.fyi/builders/CrWinClang64%28dbg%29%20tester/builds/5213

Some speculation below:

---

This is on the stack for most of the tests:

1588:6120:0512/084854.242:FATAL:gpu_channel.cc(122)] Check failed: channel_messages_.empty().
Backtrace:
	base::debug::StackTrace::StackTrace [0x00000001800E7EEE+126]
	base::debug::StackTrace::StackTrace [0x00000001800E708F+31]
	logging::LogMessage::~LogMessage [0x000000018016895E+158]
	gpu::GpuChannelMessageQueue::~GpuChannelMessageQueue [0x0000000004879B56+326]

So maybe this is related?

gpu: GPU service scheduler.

The GPU service scheduler runs tasks (closures) containing command
buffer work. Tasks are enqueued in sequences which represent indepdent
streams of execution. A task in one sequence may wait on a sync token
fence that's released on another sequence. Tasks can specify their sync
token fences beforehand so that the scheduler won't run a sequence only
to disable it due to a sync token wait. Tasks can check if they should
yield so that a higher priority task may run. If a tas
...skip...

with task traits to specify which thread a task should run on.

R=piman@chromium.org
BUG= 514813 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2814843002
Cr-Commit-Position: refs/heads/master@{#471187}

Ah, sounds like someone else made the same guess; the GPU patch is being reverted here: https://codereview.chromium.org/2881813002/

s/is getting reverted/got reverted/

And relanded 20 minutes ago: https://codereview.chromium.org/2876913003/

Perhaps the bots will clear up.

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