Failing on Win and Linux (mostly win). Errors like

PolicyTest.Disable3DAPIs (run #1):
[ RUN      ] PolicyTest.Disable3DAPIs
[5064:7164:1105/053431:INFO:media_foundation_video_encode_accelerator_win.cc(290)] Windows versions earlier than 8 are not supported.
[5064:6452:1105/053431:FATAL:gpu_channel.cc(464)] Check failed: channel_.
Backtrace:
	base::debug::StackTrace::StackTrace [0x0247BA47+23]
	logging::LogMessage::~LogMessage [0x02432321+49]
	gpu::GpuChannelMessageFilter::OnFilterRemoved [0x04DE37BB+81]
	IPC::ChannelProxy::Context::OnChannelClosed [0x030DB88F+95]
	base::internal::Invoker<base::internal::BindState<base::internal::IgnoreResultHelper<bool (__thiscall content::PlatformNotificationContextImpl::*)(void)>,scoped_refptr<content::PlatformNotificationContextImpl> >,void __cdecl(void)>::Run [0x016324BF+27]
	base::debug::TaskAnnotator::RunTask [0x024A87A8+280]
	base::MessageLoop::RunTask [0x024419EC+1228]
	base::MessageLoop::DoWork [0x02440953+611]
	base::MessagePumpForIO::DoRunLoop [0x024A9A5C+188]
	base::MessagePumpWin::Run [0x024AA4DA+74]
	base::MessageLoop::RunHandler [0x02441511+305]
	base::RunLoop::Run [0x02444289+41]
	base::Thread::Run [0x0246785D+173]
	base::Thread::ThreadMain [0x0246829E+622]
	base::PlatformThread::Sleep [0x0244EA62+290]
	BaseThreadInitThunk [0x7576336A+18]
	RtlInitializeExceptionChain [0x775592B2+99]
	RtlInitializeExceptionChain [0x77559285+54]
e:\c\win\src\chromerowser\policy\policy_browsertest.cc(1244): error: Value of: IsWebGLEnabled(contents)
  Actual: false
Expected: true
[1276:5992:1105/053431:WARNING:url_request_context_getter.cc(43)] URLRequestContextGetter leaking due to no owning thread.
[  FAILED  ] PolicyTest.Disable3DAPIs, where TypeParam =  and GetParam() =  (813 ms)

Uptick in flakes since
try run at 2016-11-05 12:48:10 UTC
history of flakes:
try run at 2016-09-06 16:53:25 UTC	(milo)	patchset	linux_chromium_rel_ng	 
try run at 2016-08-10 01:15:15 UTC	(milo)	patchset	linux_chromium_chromeos_rel_ng
Then  big batch at 
try run at 2015-03-25 04:00:22 UTC	


I don't see any recent changes in chrome/browser/policy/policy_browsertest.cc

Maybe related to r429885 "Enable WebGL 2 by default! (on desktop)" -> kainino

Or possibly related to r419329 "IPC::MessageFilter::OnFilterAdded: IPC::Sender -> IPC::Channel" -> rockot (But this is from 2016-09-17)

Gonna have to disable this without a clear culprit since it's messing up try jobs.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a5d5e38d1e12f33effaa5300409ef5d299cd3a60

commit a5d5e38d1e12f33effaa5300409ef5d299cd3a60
Author: tapted <tapted@chromium.org>
Date: Mon Nov 07 02:32:59 2016

Disable Flaky PolicyTest.Disable3DAPIs.

BUG= 662693 
TBR=bartfab@chromium.org, kainino@chromium.org

Review-Url: https://codereview.chromium.org/2477233002
Cr-Commit-Position: refs/heads/master@{#430210}

[modify] https://crrev.com/a5d5e38d1e12f33effaa5300409ef5d299cd3a60/chrome/browser/policy/policy_browsertest.cc

Detected 8 new flakes for test/step "PolicyTest.Disable3DAPIs". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyIwsSBUZsYWtlIhhQb2xpY3lUZXN0LkRpc2FibGUzREFQSXMM. This message was posted automatically by the chromium-try-flakes app.

I think this was caused by r430159

I'm sorry, this slipped through my inbox entirely somehow. I think it is unlikely to be caused by my change and agree jbauman's suggestion is more likely. 

This seems to be causing quite a few failures. tzik, ping?

Oh, sorry. I'm looking into this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8826eda8787c97736f2b671a2548dbcafd0b89aa

commit 8826eda8787c97736f2b671a2548dbcafd0b89aa
Author: tzik <tzik@chromium.org>
Date: Wed Nov 09 04:30:28 2016

Remove a DCHECK in GpuChannelMessageFilter

GpuChannelMessageFilter::OnFilterRemoved asserts |channel_| is non null.
This is no longer true after r430159 or 0e85f1d17a35bbe7, since in new code,
ChannelProxy calls MessageFilter::OnFilterRemoved even when the channel
is closed while the filter registration is pending.

This CL just removes the assertion, since null |channel_| should be harmless
here.

BUG= 662693 ,662688
CQ_INCLUDE_TRYBOTS=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/2482053002
Cr-Commit-Position: refs/heads/master@{#430862}

[modify] https://crrev.com/8826eda8787c97736f2b671a2548dbcafd0b89aa/android_webview/javatests/src/org/chromium/android_webview/test/AwContentsTest.java
[modify] https://crrev.com/8826eda8787c97736f2b671a2548dbcafd0b89aa/chrome/browser/policy/policy_browsertest.cc
[modify] https://crrev.com/8826eda8787c97736f2b671a2548dbcafd0b89aa/gpu/ipc/service/gpu_channel.cc