The first failures appears https://test-results.appspot.com/revision_range?start=624181&end=624201 but no strong culprit found.

Example failure logs:
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8923970380431275504/+/steps/network_service_content_browsertests/0/logs/DumpAccessibilityTreeTest.AccessibilityAudio__status_FAILURE_/0
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8923898649711403232/+/steps/network_service_content_browsertests/0/logs/DumpAccessibilityTreeTest.AccessibilityAudio__status_FAILURE_/0

DevTools listening on ws://127.0.0.1:42338/devtools/browser/feac13d4-5c78-4e3c-9d76-ef65479e3e5b
[24308:24308:0118/103112.865136:INFO:dump_accessibility_browsertest_base.cc(229)] File not found: /b/s/w/ir/content/test/data/accessibility/html/audio-expected-blink.txt
[24308:24308:0118/103112.865270:INFO:dump_accessibility_browsertest_base.cc(230)] No expectation file present, ignoring test on this platform. To run this test anyway, create /b/s/w/ir/content/test/data/accessibility/html/audio-expected-blink.txt (it can be empty) and then run content_browsertests with the switch: --generate-accessibility-test-expectations
[24308:24308:0118/103113.015260:INFO:dump_accessibility_browsertest_base.cc(244)] Testing: /b/s/w/ir/content/test/data/accessibility/html/audio.html
[24308:24308:0118/103113.015337:INFO:dump_accessibility_browsertest_base.cc(246)] Expected output: /b/s/w/ir/content/test/data/accessibility/html/audio-expected-auralinux.txt
../../content/browser/accessibility/dump_accessibility_browsertest_base.cc:378: Failure
Value of: is_different
  Actual: true
Expected: false
Stack trace:
#0 0x5635c44372d0 StackTraceGetter::CurrentStackTrace()
#1 0x5635c4444a67 testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#2 0x5635c44445f3 testing::internal::AssertHelper::operator=()
#3 0x5635c3a25a18 content::DumpAccessibilityTestBase::RunTestForPlatform()
#4 0x5635c3a245e9 content::DumpAccessibilityTestBase::RunTest()
#5 0x5635c3a502ed content::DumpAccessibilityTreeTest::RunHtmlTest()
#6 0x5635c3a35bbc content::DumpAccessibilityTreeTest_AccessibilityAudio_Test::RunTestOnMainThread()
#7 0x5635c5002f46 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#8 0x5635c3b6043d base::internal::FunctorTraits<>::Invoke<>()
#9 0x5635c3b603b1 base::internal::InvokeHelper<>::MakeItSo<>()
#10 0x5635c3b60357 _ZN4base8internal7InvokerINS0_9BindStateIMN7content41GenerateMHTMLAndExitRendererMessageFilterEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIS6_NSt4__Cr5tupleIJS8_EEEJLm0EEEEvOT_OT0_NSD_16integer_sequenceImJXspT1_EEEE
#11 0x5635c3c94b9c base::internal::Invoker<>::Run()
#12 0x5635c3aa86ed _ZNKR4base17RepeatingCallbackIFvvEE3RunEv
#13 0x5635c50ebd2a content::ShellBrowserMainParts::PreMainMessageLoopRun()
#14 0x7f628a7dcc27 content::BrowserMainLoop::PreMainMessageLoopRun()
#15 0x7f6289b44edd base::internal::FunctorTraits<>::Invoke<>()
#16 0x7f6289b44e51 base::internal::InvokeHelper<>::MakeItSo<>()
#17 0x7f6289b44df7 _ZN4base8internal7InvokerINS0_9BindStateIMN7content12ChildProcessEFvvEJNS0_17UnretainedWrapperIS4_EEEEEFvvEE7RunImplIS6_NSt4__Cr5tupleIJS8_EEEJLm0EEEEvOT_OT0_NSD_16integer_sequenceImJXspT1_EEEE
#18 0x7f628a56c64c base::internal::Invoker<>::Run()
#19 0x7f6289ab3bfd _ZNKR4base17RepeatingCallbackIFvvEE3RunEv
#20 0x7f628b06256c content::StartupTaskRunner::RunAllTasksNow()
#21 0x7f628a7db45f content::BrowserMainLoop::CreateStartupTasks()
#22 0x7f628a7e2cee content::BrowserMainRunnerImpl::Initialize()
#23 0x5635c50e5af0 ShellBrowserMain()
#24 0x5635c50d790a content::ShellMainDelegate::RunProcess()
#25 0x7f628bbd44ab content::RunBrowserProcessMain()
#26 0x7f628bbd5930 content::ContentMainRunnerImpl::RunServiceManager()
#27 0x7f628bbd537c content::ContentMainRunnerImpl::Run()
#28 0x7f628bbd2c19 content::ContentServiceManagerMainDelegate::RunEmbedderProcess()
#29 0x7f6272c5c73d service_manager::Main()
#30 0x7f628bbd3fd3 content::ContentMain()
#31 0x5635c5002b1f content::BrowserTestBase::SetUp()
#32 0x5635c4feb408 content::ContentBrowserTest::SetUp()
#33 0x5635c426bfae testing::internal::InvokeHelper<>::InvokeMethod<>()

[24308:24308:0118/103113.728051:ERROR:dump_accessibility_browsertest_base.cc(403)] Diff:
* Line Expected
- ---- --------
     1 [document web]
     2 ++[section]
     3 ++++[audio]
     4 ++++++[section]
     5 ++++++++[tool bar] name='audio' description='audio' horizontal
     6 ++++++++++[tool bar] name='audio' description='audio' horizontal
     7 ++++++++++++[push button] name='play' xml-roles:button
     8 ++++++++++++[text] name='0:00'
     9 ++++++++++++[text] name='/ 0:00'
    10 ++++++++++++[slider] description='audio time scrubber' horizontal xml-roles:slider
    11 ++++++++++++[section]
    12 ++++++++++++++[section]
*   13 ++++++++++++++[push button] name='mute' xml-roles:button
*   14 <-- End-of-file -->

Actual
------
[document web]
++[section]
++++[audio]
++++++[section]
++++++++[tool bar] name='audio' description='audio' horizontal
++++++++++[tool bar] name='audio' description='audio' horizontal
++++++++++++[push button] name='play' xml-roles:button
++++++++++++[text] name='0:00'
++++++++++++[text] name='/ 0:00'
++++++++++++[slider] description='audio time scrubber' horizontal xml-roles:slider
++++++++++++[section]
++++++++++++++[section]
++++++++++++++[slider] name='volume' horizontal xml-roles:slider
++++++++++++++[push button] name='mute' xml-roles:button
++++++++++++[push button] name='show more media controls' description='more options' xml-roles:button
<-- End-of-file -->