From logs:
[ RUN      ] ParallelDownloadTest.ParallelDownloadResumption
Xlib:  extension "RANDR" missing on display ":99".
DevTools listening on ws://127.0.0.1:48723/devtools/browser/2e7f4219-f0b6-4880-a352-6074bb5cc1b6
BrowserTestBase received signal: Terminated. Backtrace:
#0 0x000001d707b7 base::debug::StackTrace::StackTrace()
#1 0x000001ad79e1 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7f2983527cb0 <unknown>
#3 0x7f29835e1c5d __poll
#4 0x7f29875e4fe4 <unknown>
#5 0x7f29875e50ec g_main_context_iteration
#6 0x000001d893a6 base::MessagePumpGlib::Run()
#7 0x000001da1230 base::RunLoop::Run()
#8 0x000001aeeafe content::RunMessageLoop()
#9 0x000001addedb content::DownloadUpdatedObserver::WaitForEvent()
#10 0x000000532198 content::ParallelDownloadTest_ParallelDownloadResumption_Test::RunTestOnMainThread()
#11 0x000001ad7742 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#12 0x000001b346bd content::ShellBrowserMainParts::PreMainMessageLoopRun()
#13 0x0000015f9cdd content::BrowserMainLoop::PreMainMessageLoopRun()
#14 0x00000191eea7 content::StartupTaskRunner::RunAllTasksNow()
#15 0x0000015f813d content::BrowserMainLoop::CreateStartupTasks()
#16 0x0000015fc776 content::BrowserMainRunnerImpl::Initialize()
#17 0x000001b1bd45 ShellBrowserMain()
#18 0x000001b14f2d content::ShellMainDelegate::RunProcess()
#19 0x000001543467 content::RunNamedProcessTypeMain()
#20 0x000001543ebd content::ContentMainRunnerImpl::Run()
#21 0x000002be5a24 service_manager::Main()
#22 0x000000da1172 content::ContentMain()
#23 0x000001ad7423 content::BrowserTestBase::SetUp()
#24 0x000001ace9be content::ContentBrowserTest::SetUp()
#25 0x00000053374e content::(anonymous namespace)::ParallelDownloadTest::SetUp()
#26 0x000000a2508e testing::Test::Run()
#27 0x000000a25b00 testing::TestInfo::Run()
#28 0x000000a25fe7 testing::TestCase::Run()
#29 0x000000a2c417 testing::internal::UnitTestImpl::RunAllTests()
#30 0x000000a2c0a3 testing::UnitTest::Run()
#31 0x000001afa144 base::TestSuite::Run()
#32 0x000001ad1c93 content::ContentTestLauncherDelegate::RunTestSuite()
#33 0x000001ae9c73 content::LaunchTests()
#34 0x000001ad1c42 main
#35 0x7f2983512f45 __libc_start_main
#36 0x000000487010 <unknown>

Running findit.

Findit found the flake started in build 61508 of the config "chromium.linux / Linux Tests"
with confidence 100.0% based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyxQELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKOAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzLzYxNTE1L2Jyb3dzZXJfc2lkZV9uYXZpZ2F0aW9uX2NvbnRlbnRfYnJvd3NlcnRlc3RzL1VHRnlZV3hzWld4RWIzZHViRzloWkZSbGMzUXVVR0Z5WVd4c1pXeEViM2R1Ykc5aFpGSmxjM1Z0Y0hScGIyND0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).
Flake Analyzer is in alpha version.
Feedback is welcome using component Tools>Test>FindIt>Flakiness !

Assigning to xingliu@ based on FindIt findings above.

Findit blames it on https://chromium.googlesource.com/chromium/src/+/adf37191953b687857d1224890ffa8148174e974

Updating the bug title. Findit graph shows that it passes 60% time.

Will disable the test for short term soon.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f8829cc56d65fe592958dd382ba44befe0c224da

commit f8829cc56d65fe592958dd382ba44befe0c224da
Author: Xing Liu <xingliu@chromium.org>
Date: Wed Aug 30 20:13:05 2017

Disable flaky test ParallelDownloadTest.ParallelDownloadResumption

It's currently flaky on try bots for unknown reason, disable for now.


Bug:  760384 
Change-Id: I607e2e624349aa1c307e0711b363df7dc3cbc77f
Reviewed-on: https://chromium-review.googlesource.com/643550
Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Xing Liu <xingliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#498584}
[modify] https://crrev.com/f8829cc56d65fe592958dd382ba44befe0c224da/content/browser/download/download_browsertest.cc

Findit found the flake started in build 61515 of the config "chromium.linux / Linux Tests"
with confidence 100.0% based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyxQELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKOAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzLzYxNTE1L2Jyb3dzZXJfc2lkZV9uYXZpZ2F0aW9uX2NvbnRlbnRfYnJvd3NlcnRlc3RzL1VHRnlZV3hzWld4RWIzZHViRzloWkZSbGMzUXVVR0Z5WVd4c1pXeEViM2R1Ykc5aFpGSmxjM1Z0Y0hScGIyND0MCxITTWFzdGVyRmxha2VBbmFseXNpcxgEDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).
Flake Analyzer is in alpha version.
Feedback is welcome using component Tools>Test>FindIt>Flakiness !