Stack trace:

[ RUN      ] DumpAccessibilityTreeTest.AccessibilitySource
Xlib:  extension "RANDR" missing on display ":100".

DevTools listening on ws://127.0.0.1:35798/devtools/browser/4b73399f-28f7-40c4-bd62-b7a2a16cc248
[20012:20012:0111/115701.287512:INFO:dump_accessibility_browsertest_base.cc(230)] File not found: /b/s/w/ir/content/test/data/accessibility/html/source-expected-blink.txt
[20012:20012:0111/115701.287650:INFO:dump_accessibility_browsertest_base.cc(231)] No expectation file present, ignoring test on this platform. To run this test anyway, create /b/s/w/ir/content/test/data/accessibility/html/source-expected-blink.txt (it can be empty) and then run content_browsertests with the switch: --generate-accessibility-test-expectations
[20012:20012:0111/115701.784161:INFO:dump_accessibility_browsertest_base.cc(245)] Testing: /b/s/w/ir/content/test/data/accessibility/html/source.html
[20012:20012:0111/115701.784277:INFO:dump_accessibility_browsertest_base.cc(247)] Expected output: /b/s/w/ir/content/test/data/accessibility/html/source-expected-auralinux.txt
../../content/browser/accessibility/dump_accessibility_browsertest_base.cc:379: Failure
Value of: is_different
  Actual: true
Expected: false
Stack trace:
#0 0x000057809e89 StackTraceGetter::CurrentStackTrace()
#1 0x00005781d764 testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#2 0x00005781d15e testing::internal::AssertHelper::operator=()
#3 0x000056846360 content::DumpAccessibilityTestBase::RunTestForPlatform()
#4 0x0000568445c7 content::DumpAccessibilityTestBase::RunTest()
#5 0x00005685b664 content::DumpAccessibilityTreeTest::RunHtmlTest()
#6 0x00005685a271 content::DumpAccessibilityTreeTest_AccessibilitySource_Test::RunTestOnMainThread()
#7 0x0000588eed44 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#8 0x0000569eeb97 base::internal::FunctorTraits<>::Invoke<>()
#9 0x0000569eead3 base::internal::InvokeHelper<>::MakeItSo<>()
#10 0x0000588f23bf _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserTestBaseEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIRKS6_RKNSt4__Cr5tupleIJS8_EEEJLj0EEEEvOT_OT0_NSF_16integer_sequenceIjJXspT1_EEEE
#11 0x0000588f229a base::internal::Invoker<>::Run()
#12 0x0000568d69a1 _ZNKR4base17RepeatingCallbackIFvvEE3RunEv
#13 0x000058af2fa0 content::ShellBrowserMainParts::PreMainMessageLoopRun()
#14 0x0000ebe0f95d content::BrowserMainLoop::PreMainMessageLoopRun()
#15 0x0000eaac3c77 base::internal::FunctorTraits<>::Invoke<>()
#16 0x0000eaac3bb3 base::internal::InvokeHelper<>::MakeItSo<>()
#17 0x0000ebe1935f _ZN4base8internal7InvokerINS0_9BindStateIMN7content15BrowserMainLoopEFivEJNS0_17UnretainedWrapperIS4_EEEEEFivEE7RunImplIRKS6_RKNSt4__Cr5tupleIJS8_EEEJLj0EEEEiOT_OT0_NSF_16integer_sequenceIjJXspT1_EEEE
#18 0x0000ebe1923a base::internal::Invoker<>::Run()
#19 0x0000ea9e3c81 _ZNKR4base17RepeatingCallbackIFvvEE3RunEv
#20 0x0000ecdd4051 content::StartupTaskRunner::RunAllTasksNow()
#21 0x0000ebe0d7a0 content::BrowserMainLoop::CreateStartupTasks()
#22 0x0000ebe1c610 content::BrowserMainRunnerImpl::Initialize()
#23 0x000058a77091 ShellBrowserMain()
#24 0x000058a6d6ce content::ShellMainDelegate::RunProcess()
#25 0x0000ee12ce6d content::RunBrowserProcessMain()
#26 0x0000ee12e872 content::ContentMainRunnerImpl::RunServiceManager()
#27 0x0000ee12e15e content::ContentMainRunnerImpl::Run()
#28 0x0000ee12a72d content::ContentServiceManagerMainDelegate::RunEmbedderProcess()
#29 0x0000d0afc12b service_manager::Main()
#30 0x0000ee12c816 content::ContentMain()
#31 0x0000588ee75a content::BrowserTestBase::SetUp()
#32 0x0000588c419a content::ContentBrowserTest::SetUp()
#33 0x0000574ea85b testing::internal::InvokeHelper<>::InvokeMethod<>()

[20012:20012:0111/115702.697761:ERROR:dump_accessibility_browsertest_base.cc(404)] Diff:
* Line Expected
- ---- --------
     1 [document web] focusable focused
     2 ++[section]
     3 ++++[audio] focusable
     4 ++++++[section]
     5 ++++++++[tool bar] name='audio' description='audio' horizontal
     6 ++++++++++[tool bar] name='audio' description='audio' horizontal
     7 ++++++++++++[push button] name='play' focusable
     8 ++++++++++++[text] name='0:00'
     9 ++++++++++++[text] name='/ 0:00'
    10 ++++++++++++[slider] description='audio time scrubber' focusable horizontal
    11 ++++++++++++[section]
    12 ++++++++++++++[section]
*   13 ++++++++++++++[push button] name='mute'
    14 <-- End-of-file -->

Actual
------
[document web] focusable focused
++[section]
++++[audio] focusable
++++++[section]
++++++++[tool bar] name='audio' description='audio' horizontal
++++++++++[tool bar] name='audio' description='audio' horizontal
++++++++++++[push button] name='play' focusable
++++++++++++[text] name='0:00'
++++++++++++[text] name='/ 0:00'
++++++++++++[slider] description='audio time scrubber' focusable horizontal
++++++++++++[section]
++++++++++++++[section]
++++++++++++++[push button] name='mute' focusable
<-- End-of-file -->

Flakiness dashboard: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=content_browsertests&tests=DumpAccessibilityTreeTest.AccessibilitySource%0A

Example failing build: https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Linux%20Tests%20%28dbg%29%281%29%2832%29/55621