When UAv2 is enabled, the test fails at this assert on the bot (linux_chromium_rel_ng) even though it runs fine locally:
https://cs.chromium.org/chromium/src/chrome/browser/ui/blocked_content/popup_blocker_browsertest.cc?rcl=79cdbe699c94370dbfd155b6f84410e0d671f496&l=305

Below is the failure log from 
https://logs.chromium.org/v/?s=chromium%2Fbuildbucket%2Fcr-buildbucket.appspot.com%2F8942457265856329840%2F%2B%2Fsteps%2Finteractive_ui_tests__with_patch_%2F0%2Flogs%2FPopupBlockerBrowserTest.PopupPositionMetrics%2F0

[ RUN      ] PopupBlockerBrowserTest.PopupPositionMetrics
Xlib:  extension "RANDR" missing on display ":99".
[17935:17971:0628/102232.799080:ERROR:bus.cc(394)] Failed to connect to the bus: Could not parse server address: Unknown address type (examples of valid types are "tcp" and on UNIX "unix")
[17935:17935:0628/102232.804334:WARNING:password_store_factory.cc(250)] 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.
(interactive_ui_tests:17935): LIBDBUSMENU-GLIB-WARNING **: Unable to get session bus: Unknown or unsupported transport 'disabled' for address 'disabled:'
[17935:17935:0628/102232.892714:WARNING:gaia_auth_fetcher.cc(902)] Could not reach Google Accounts servers: errno -11
[17935:18008:0628/102232.964607:WARNING:embedded_test_server.cc(229)] Request not handled. Returning 404: /favicon.ico
(interactive_ui_tests:17935): LIBDBUSMENU-GLIB-WARNING **: Unable to get session bus: Unknown or unsupported transport 'disabled' for address 'disabled:'
../../chrome/browser/ui/blocked_content/popup_blocker_browsertest.cc:305: Failure
Expected equality of these values:
  4
  GetBlockedContentsCount()
    Which is: 3
Stack trace:
#0 0x0000023fdd7c testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop()
#1 0x0000023fd759 testing::internal::AssertHelper::operator=()
#2 0x0000021cad4b (anonymous namespace)::PopupBlockerBrowserTest_PopupPositionMetrics_Test::RunTestOnMainThread()
#3 0x0000051775c0 content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#4 0x000004cf38bf ChromeBrowserMainParts::PreMainMessageLoopRunImpl()
#5 0x000004cf251a ChromeBrowserMainParts::PreMainMessageLoopRun()
#6 0x0000031989d1 content::BrowserMainLoop::PreMainMessageLoopRun()
#7 0x00000366db05 content::StartupTaskRunner::RunAllTasksNow()
#8 0x000003197129 content::BrowserMainLoop::CreateStartupTasks()
#9 0x00000319b775 content::BrowserMainRunnerImpl::Initialize()
#10 0x0000031949c5 content::BrowserMain()
#11 0x000004cb8db5 content::RunBrowserProcessMain()
#12 0x000004cb9d91 content::ContentMainRunnerImpl::Run()
#13 0x000006ca587f service_manager::Main()
#14 0x000004cb7d24 content::ContentMain()
#15 0x000005177126 content::BrowserTestBase::SetUp()
#16 0x000004cdca42 InProcessBrowserTest::SetUp()