Actually it also failed in https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/62671.

The error log from the first three builds mentioned in #0 and build/62671:
=== LOG STARTS ===
[ RUN      ] SBNavigationObserverBrowserTest.DirectDownloadNoReferrerTargetBlank
Xlib:  extension "RANDR" missing on display ":99".
[31936:31936:0426/010433.282694:WARNING:audio_manager.cc(293)] Multiple instances of AudioManager detected
[31936:31936:0426/010433.282795:WARNING:audio_manager.cc(254)] Multiple instances of AudioManager detected
[31936:31936:0426/010433.619006:WARNING:password_store_factory.cc(249)] Using basic (unencrypted) store for password storage. See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_password_storage.md for more information about password storage options.
[31936:32025:0426/010435.126632:WARNING:simple_synchronous_entry.cc(1051)] Could not open platform files for entry.
[31936:32096:0426/010435.501727:WARNING:embedded_test_server.cc(219)] Request not handled. Returning 404: /favicon.ico
../../chrome/browser/safe_browsing/safe_browsing_navigation_observer_browsertest.cc:228: Failure
Value of: download_items.size()
  Actual: 0
Expected: 1U
Which is: 1
../../build/linux/debian_jessie_amd64-sysroot/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/debug/vector:346:
    error: attempt to subscript container with out-of-bounds index 0, but
    container only holds 0 elements.

Objects involved in the operation:
sequence "this" @ 0x0x7fffbcf5fbe0 {
}
Received signal 6
#0 0x7f1c794fb72b base::debug::StackTrace::StackTrace()
#1 0x7f1c794fa42c base::debug::StackTrace::StackTrace()
#2 0x7f1c794fb23f base::debug::(anonymous namespace)::StackDumpSignalHandler()
#3 0x7f1c79983330 <unknown>
#4 0x7f1c60435c37 gsignal
#5 0x7f1c60439028 abort
#6 0x7f1c60874fe5 __gnu_debug::_Error_formatter::_M_error()
#7 0x000000868a1c std::__debug::vector<>::operator[]()
#8 0x0000016ccaf3 safe_browsing::SBNavigationObserverBrowserTest::GetDownload()
#9 0x0000016be7dc safe_browsing::SBNavigationObserverBrowserTest_DirectDownloadNoReferrerTargetBlank_Test::RunTestOnMainThread()
#10 0x000003e81c38 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#11 0x000000896d75 _ZN4base8internal13FunctorTraitsIM25RenderViewContextMenuBaseFvvEvE6InvokeIP21RenderViewContextMenuJEEEvS4_OT_DpOT0_
#12 0x000000896c81 _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIM25RenderViewContextMenuBaseFvvEJP21RenderViewContextMenuEEEvOT_DpOT0_
#13 0x000003e83617 _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserTestBaseEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEvOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#14 0x000003e8355c _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserTestBaseEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE3RunEPNS0_13BindStateBaseE
#15 0x00000087dd8d _ZNKR4base8CallbackIFvvELNS_8internal8CopyModeE1ELNS2_10RepeatModeE1EE3RunEv
#16 0x00000399282e ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#17 0x000003991280 ChromeBrowserMainParts::PreMainMessageLoopRun()
#18 0x7f1c70a65101 content::BrowserMainLoop::PreMainMessageLoopRun()
#19 0x7f1c6fcd1a75 _ZN4base8internal13FunctorTraitsIMN7content13URLLoaderImplEFvvEvE6InvokeIPS3_JEEEvS5_OT_DpOT0_
#20 0x7f1c70a6e941 _ZN4base8internal12InvokeHelperILb0EiE8MakeItSoIRKMN7content15BrowserMainLoopEFivEJPS5_EEEiOT_DpOT0_
#21 0x7f1c70a6e8e7 _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserMainLoopEFivEJNS0_17UnretainedWrapperIS4_EEEEEFivEE7RunImplIRKS6_RKSt5tupleIJS8_EEJLm0EEEEiOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#22 0x7f1c70a6e82c _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserMainLoopEFivEJNS0_17UnretainedWrapperIS4_EEEEEFivEE3RunEPNS0_13BindStateBaseE
#23 0x7f1c6fcaad7d _ZNKR4base8CallbackIFvvELNS_8internal8CopyModeE1ELNS2_10RepeatModeE1EE3RunEv
#24 0x7f1c71649b3b content::StartupTaskRunner::RunAllTasksNow()
#25 0x7f1c70a62c00 content::BrowserMainLoop::CreateStartupTasks()
#26 0x7f1c70a71b57 content::BrowserMainRunnerImpl::Initialize()
#27 0x7f1c70a5eeaf content::BrowserMain()
#28 0x7f1c72319756 content::RunNamedProcessTypeMain()
#29 0x7f1c7231ba8d content::ContentMainRunnerImpl::Run()
#30 0x7f1c7231827a content::ContentServiceManagerMainDelegate::RunEmbedderProcess()
#31 0x7f1c652a43d9 service_manager::Main()
#32 0x7f1c723191af content::ContentMain()
#33 0x000003e8192e content::BrowserTestBase::SetUp()
#34 0x000002ce80a0 InProcessBrowserTest::SetUp()
#35 0x000001152f6e _ZN7testing8internal12InvokeHelperIvSt5tupleIJEEE12InvokeMethodI14ServiceProcessMS6_FvvEEEvPT_T0_RKS3_
#36 0x00000403ccc2 testing::internal::HandleExceptionsInMethodIfSupported<>()
#37 0x000004031ab4 testing::Test::Run()
#38 0x0000040322bd testing::TestInfo::Run()
#39 0x00000403285f testing::TestCase::Run()
#40 0x000004037bcc testing::internal::UnitTestImpl::RunAllTests()
#41 0x00000115256e _ZN7testing8internal12InvokeHelperIbSt5tupleIJEEE12InvokeMethodI20MockServiceIPCServerMS6_FbvEEEbPT_T0_RKS3_
#42 0x00000403e382 testing::internal::HandleExceptionsInMethodIfSupported<>()
#43 0x00000403786f testing::UnitTest::Run()
#44 0x000002d05731 RUN_ALL_TESTS()
#45 0x000002d04422 base::TestSuite::Run()
#46 0x000002ca3750 ChromeTestSuiteRunner::RunTestSuite()
#47 0x000002ca3849 ChromeTestLauncherDelegate::RunTestSuite()
#48 0x000003f163ef content::LaunchTests()
#49 0x000002ca3b79 LaunchChromeTests()
#50 0x000002ca3005 main
#51 0x7f1c60420f45 __libc_start_main
#52 0x0000007f4e64 <unknown>
  r8: 00007f1c607bf9d0  r9: 00007fffbcf5f6c8 r10: 0000000000000008 r11: 0000000000000206
 r12: 0000000000000003 r13: 00007fffbcf63bd0 r14: 0000000000000000 r15: 0000000000000000
  di: 0000000000007cc0  si: 0000000000007cc0  bp: 00007fffbcf5f9f0  bx: 00007fffbcf5f938
  dx: 0000000000000006  ax: 0000000000000000  cx: ffffffffffffffff  sp: 00007fffbcf5f718
  ip: 00007f1c60435c37 efl: 0000000000000206 cgf: 0000000000000033 erf: 0000000000000000
 trp: 0000000000000000 msk: 0000000000000000 cr2: 0000000000000000
[end of stack trace]
=== LOG ENDS ===

Among the last 200 builds, this test fails in  https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29/builds/62662 for the first time.

The tests itself was touched 4 weeks ago last time.

In 62662 there was a revert of https://codereview.chromium.org/2788323002/ "SafeBrowsing: update interstitial layouts" (the revert CL is https://codereview.chromium.org/2842633002). Out of that batch this is the only somewhat related CL.

ntfschr@, can this revert be related to the test above?

csharrison, should this be duped into  issue 709508 ?

Yes looks like it.

Also, see this issue on Mac

https://uberchromegw.corp.google.com/i/chromium.mac/builders/Mac10.11%20Tests/builds/11622

Sorry for the late reply. This log looks unrelated to my CL--mine had to do with visibility of DOM nodes.