This has been failing for a while now, at least as far back as 200 builds (I didn't look further). Here's sample output:

[ RUN      ] SitePerProcessHitTestBrowserTest.CrossProcessMouseCapture/0
[27689:27837:0727/082547.614662:ERROR:network_service.cc(66)] Not implemented reached in std::unique_ptr<net::NetworkChangeNotifier> network::(anonymous namespace)::CreateNetworkChangeNotifierIfNeeded()
DevTools listening on ws://127.0.0.1:38630/devtools/browser/1d7d7acf-a87f-4b8b-b720-5eaf4d90a994
[27689:27689:0727/082547.645710:ERROR:proxy_resolution_service.cc(1528)] ProxyConfigService for ChromeOS should be created in profile_io_data.cc::CreateProxyConfigService and this should be used only for examples.
BrowserTestBase received signal: Terminated. Backtrace:
#0 0x00000277399c base::debug::StackTrace::StackTrace()
#1 0x0000023de625 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7f4301824cb0 <unknown>
#3 0x7f43018ec6d3 epoll_wait
#4 0x00000279f9dd epoll_dispatch
#5 0x00000279d4bc event_base_loop
#6 0x000002782971 base::MessagePumpLibevent::Run()
#7 0x000002722fa5 base::RunLoop::Run()
#8 0x0000023e39c3 content::InputEventAckWaiter::Wait()
#9 0x000000a1435d content::SitePerProcessHitTestBrowserTest_CrossProcessMouseCapture_Test::RunTestOnMainThread()
#10 0x0000023ddb9b content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#11 0x000002445688 content::ShellBrowserMainParts::PreMainMessageLoopRun()
#12 0x000001d74251 content::BrowserMainLoop::PreMainMessageLoopRun()
#13 0x0000020d5c17 content::StartupTaskRunner::RunAllTasksNow()
#14 0x000001d72c3d content::BrowserMainLoop::CreateStartupTasks()
#15 0x000001d76553 content::BrowserMainRunnerImpl::Initialize()
#16 0x00000242db99 ShellBrowserMain()
#17 0x00000242427f content::ShellMainDelegate::RunProcess()
#18 0x000001cb047e content::ContentMainRunnerImpl::Run()
#19 0x000003974110 service_manager::Main()
#20 0x000001459264 content::ContentMain()
#21 0x0000023dd7d2 content::BrowserTestBase::SetUp()
#22 0x0000023d3bdf content::ContentBrowserTest::SetUp()
#23 0x00000121ed0d testing::Test::Run()
#24 0x00000121f930 testing::TestInfo::Run()
#25 0x00000121fe47 testing::TestCase::Run()
#26 0x00000122b347 testing::internal::UnitTestImpl::RunAllTests()
#27 0x00000122aebd testing::UnitTest::Run()
#28 0x000002409791 base::TestSuite::Run()
#29 0x0000023d74aa content::ContentTestLauncherDelegate::RunTestSuite()
#30 0x0000023f397e content::LaunchTests()
#31 0x0000023d7470 main
#32 0x7f430180ff45 __libc_start_main
#33 0x00000053d00a _start

I think the test is timing out.

Given this has been happening for a while, I'm doing to DISABLE.

Assigning to Ria as she seems to have either written the test, or substantially changed it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/23b14a8f754bf939b9a704806b0e7853ba519880

commit 23b14a8f754bf939b9a704806b0e7853ba519880
Author: Scott Violet <sky@chromium.org>
Date: Fri Jul 27 17:01:24 2018

chromeos: disables SitePerProcessHitTestBrowserTest.CrossProcessMouseCapture

It's flakey, and has been flakey for quite a while.

BUG= 868409 
TEST=test only change
TBR=riajiang@chromium.org

Change-Id: I4d4a57c9eed04563cdad114075c197244ea7ccdd
Reviewed-on: https://chromium-review.googlesource.com/1153207
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578679}
[modify] https://crrev.com/23b14a8f754bf939b9a704806b0e7853ba519880/content/browser/site_per_process_hit_test_browsertest.cc

This is flaky on other platforms as well (FYI so you don't run down platform-specific code trying to fix it), just not flaky enough to seemingly fail the bots on any retries. I'll remove this from the sheriff list, but here's an example of Win10 and Linux failures:

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8940021224905215648/+/steps/content_browsertests__experimental__on_Windows-10-15063/0/stdout

https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8940142623000925440/+/steps/content_browsertests/0/stdout

This passed on retries, and doesn't seem to have failed any other bots recently, so I'll still let this only be disabled on CrOS. Removing the sheriff label for now.

Flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=content_browsertests&tests=SitePerProcessHitTestBrowserTest.CrossProcessMouseCapture