First failing build: https://ci.chromium.org/buildbot/chromium.fyi/Mojo%20ChromiumOS/26451

I don't see any suspicious CLs in that build, so I suspect something earlier introduced flake.

Other PDFExtension tests flakily time out as well.

[ RUN      ] PDFExtensionClipboardTest.IndividualShiftLeftArrowPresses
[27887:27887:0130/034119.897757:WARNING:chrome_browser_main_chromeos.cc(597)] Running as stub user with profile dir: test-user
[27887:28023:0130/034120.593564:ERROR:logging_chrome.cc(218)] Unable to create symlink /b/s/w/itwU_2a4/.org.chromium.Chromium.ErrCc5/dvw7XHV/test-user/chrome_debug.log pointing at /b/s/w/itwU_2a4/.org.chromium.Chromium.ErrCc5/dvw7XHV/test-user/chrome_debug_20180130-034120: No such file or directory (2)
[27887:27887:0130/034120.667482:WARNING:user_session_manager.cc(1050)] Attempting to save user password for non enterprise user.
[27887:27887:0130/034120.780594:ERROR:delegated_frame_host.cc(232)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[27887:27887:0130/034120.895606:ERROR:wallpaper_controller.cc(1228)] User is ephemeral or guest! Fallback to default wallpaper.
[27887:28051:0130/034120.982729:WARNING:simple_synchronous_entry.cc(1217)] Could not open platform files for entry.
[27887:27887:0130/034121.021759:ERROR:delegated_frame_host.cc(232)] Not implemented reached in void content::DelegatedFrameHost::SetNeedsBeginFrames(bool)
[27887:28102:0130/034121.031743:WARNING:embedded_test_server.cc(228)] Request not handled. Returning 404: /favicon.ico
[27887:27887:0130/034121.145128:INFO:CONSOLE(0)] "Styling master document from stylesheets defined in HTML Imports is deprecated, and is planned to be removed in M65, around March 2018. Please refer to https://goo.gl/EGXzpw for possible migration paths.", source:  (0)
[1:1:0130/034121.985083:WARNING:resource_message_handler.cc(49)] 'Post' message handler failed to complete successfully.
BrowserTestBase received signal: Terminated. Backtrace:
#0 0x000003e89b0c base::debug::StackTrace::StackTrace()
#1 0x0000044cf5a2 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7f76e528dcb0 <unknown>
#3 0x7f76e5355693 epoll_wait
#4 0x000004e2593d epoll_dispatch
#5 0x000004e2341d event_base_loop
#6 0x000003eadc7e base::MessagePumpLibevent::Run()
#7 0x000003eaafd9 base::MessageLoop::Run()
#8 0x000003ed5c09 base::RunLoop::Run()
#9 0x000004508d00 content::RunAllPendingInMessageLoop()
#10 0x00000096e945 PDFExtensionClipboardTest::CheckClipboard()
#11 0x000000966746 PDFExtensionClipboardTest_IndividualShiftLeftArrowPresses_Test::RunTestOnMainThread()
#12 0x0000044cf2f5 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#13 0x000003fbd719 ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#14 0x000003fbc4ad ChromeBrowserMainParts::PreMainMessageLoopRun()
#15 0x000001982fb8 chromeos::ChromeBrowserMainPartsChromeos::PreMainMessageLoopRun()
#16 0x000002731c11 content::BrowserMainLoop::PreMainMessageLoopRun()
#17 0x000002b699d5 content::StartupTaskRunner::RunAllTasksNow()
#18 0x00000272ffbd content::BrowserMainLoop::CreateStartupTasks()
#19 0x000002734b23 content::BrowserMainRunnerImpl::Initialize()
#20 0x00000272db92 content::BrowserMain()
#21 0x000003e56c82 content::ContentMainRunnerImpl::Run()
#22 0x0000060f797b service_manager::Main()
#23 0x000003e55264 content::ContentMain()
#24 0x0000044cef5f content::BrowserTestBase::SetUp()
#25 0x000003f753bc InProcessBrowserTest::SetUp()

Maybe related to  issue 763452  or  issue 787945 ?

jonross, can you help route this to the right person?