First failing build:
https://uberchromegw.corp.google.com/i/chromiumos.chromium/builders/x86-generic-telemetry/builds/11042

Stack:
11/24 22:49:52.770 INFO |run_chromeos_tests:0052| [339/1062] telemetry.internal.browser.extension_unittest.WebviewInExtensionTest.testWebviewInExtension failed unexpectedly 20.8130s:
11/24 22:49:52.770 INFO |run_chromeos_tests:0052|   Traceback (most recent call last):
11/24 22:49:52.771 INFO |run_chromeos_tests:0052|     File "/usr/local/telemetry/src/third_party/catapult/telemetry/telemetry/internal/browser/extension_unittest.py", line 217, in testWebviewInExtension
11/24 22:49:52.771 INFO |run_chromeos_tests:0052|       self.assertEquals(1, len(webview_contexts))
11/24 22:49:52.771 INFO |run_chromeos_tests:0052|   AssertionError: 1 != 0

Failing assert is this one:
https://cs.chromium.org/chromium/src/third_party/catapult/telemetry/telemetry/internal/browser/extension_unittest.py?l=218