Also all DomSerializerTests tests

Also: IndexedDBBrowserTestSingleProcess.RenderThreadShutdownTest

Also: RenderThreadImplDiscardableMemoryBrowserTest.*

Also:   RenderViewBrowserTest.ConfirmCacheInformationPlumbed

Also: ResourceFetcherTests.*

Also: SavableResourcesTest.*

This is occurring because while GpuChildThread creates VizMainImpl, it never calls TearDown.

This is tricky though.
  -  InProcessGpuThread is creating VizMainImpl on the gpu thread
  -  InProcessGpuThread would be attempting to tear down VizMainImpl on the gpu thread.
  -  There is a race/blocking condition between the gpu and compositor threads. Due to this we need both advancing for tear down to work correctly.

So we need another thread to actually call VizMainImpl::TearDown in this situation.

Initialization stack:
  viz::VizMainImpl::VizMainImpl()
  content::GpuChildThread::GpuChildThread()
  content::GpuChildThread::GpuChildThread()
  content::InProcessGpuThread::Init()
  base::Thread::ThreadMain()
  base::(anonymous namespace)::ThreadFunc()
  start_thread
  clone

Shutdown stack:
  viz::VizMainImpl::~VizMainImpl()
  content::GpuChildThread::~GpuChildThread()
  content::GpuChildThread::~GpuChildThread()
  content::GpuChildThread::~GpuChildThread()
  content::ChildProcess::~ChildProcess()
  content::GpuProcess::~GpuProcess()
  content::GpuProcess::~GpuProcess()
  content::InProcessGpuThread::CleanUp()
  base::Thread::ThreadMain()
  base::(anonymous namespace)::ThreadFunc()
  start_thread
  clone

Passing to sadrul@ after discussions.

Also happened in a new test that was added, for some reason the cq didn't block it from landing

WebRtcCaptureFromElementBrowserTest.CaptureFromCanvas2DHandlesContextLoss

I'll take a look at this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e004637353199f8588dcf2f4510923905af0aea4

commit e004637353199f8588dcf2f4510923905af0aea4
Author: kylechar <kylechar@chromium.org>
Date: Thu Feb 01 01:19:10 2018

viz: Shutdown properly with OOP-D.

Change GpuChildThread to shutdown VizMainImpl cleanly. VizMainImpl needs
to shutdown the GPU and compositor thread in a specific order, however
the implementation of VizMainImpl::TearDown() requird that it be called
from a third thread.

Reorder the VizMainImpl::Teardown() logic so it can be called from the
GPU thread and move it to the destructor. Remove most WaitableEvent
usage since we can rely on Thread::Stop() to synchronize with thread
destruction.

Also simplify GpuHost and WindowServer destruction.

Bug:  785023 
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: Idbac0d6b91fc32b403a359fdcf3d7ea62c17f682
Reviewed-on: https://chromium-review.googlesource.com/893520
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533509}
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/components/viz/service/main/viz_main_impl.cc
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/components/viz/service/main/viz_main_impl.h
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/content/gpu/gpu_child_thread.cc
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/services/ui/ws/gpu_host.cc
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/services/ui/ws/gpu_host.h
[modify] https://crrev.com/e004637353199f8588dcf2f4510923905af0aea4/services/ui/ws/window_server.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f55fc4750c0f574c4dfe246e2cb10587e26a5d04

commit f55fc4750c0f574c4dfe246e2cb10587e26a5d04
Author: kylechar <kylechar@chromium.org>
Date: Thu Feb 01 16:42:30 2018

viz: Enable more viz_content_browsertests.

VizMainImpl thread shutdown issues have been fixed. Enabled tests that
were disabled because of that problem.

Bug:  785023 
Change-Id: I6dc21fabbfaacd7d0e458fb06697b03651a3f396
Reviewed-on: https://chromium-review.googlesource.com/893534
Commit-Queue: kylechar <kylechar@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533698}
[modify] https://crrev.com/f55fc4750c0f574c4dfe246e2cb10587e26a5d04/testing/buildbot/filters/mojo.fyi.viz.content_browsertests.filter
[modify] https://crrev.com/f55fc4750c0f574c4dfe246e2cb10587e26a5d04/testing/buildbot/filters/viz.content_browsertests.filter

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df

commit 7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df
Author: kylechar <kylechar@chromium.org>
Date: Mon Feb 05 18:04:13 2018

Enable mus_content_browertests.

Enable passing tests and delete the now empty filter file.

Bug:  785023 
Change-Id: If1163fe391621e7d15f3b9d2f1be573bec1498e5
Reviewed-on: https://chromium-review.googlesource.com/901772
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534421}
[modify] https://crrev.com/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df/testing/buildbot/chromium.chromiumos.json
[modify] https://crrev.com/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df/testing/buildbot/chromium.fyi.json
[modify] https://crrev.com/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df/testing/buildbot/chromium.memory.json
[modify] https://crrev.com/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df/testing/buildbot/filters/BUILD.gn
[delete] https://crrev.com/fd945fc5e37b4f14bf08fcc07169121ddff129ff/testing/buildbot/filters/mus.content_browsertests.filter
[modify] https://crrev.com/7873e8dbfcd5bf2e5e05ab75a204e78ffabf78df/testing/buildbot/test_suites.pyl