The error:

[ RUN      ] ComponentToolbarActionsBrowserTest.ComponentToolbarActionsShowUpAndRespondToClicks
[12490:12490:0326/193206.447766:WARNING:chrome_browser_main_chromeos.cc(618)] Running as stub user with profile dir: test-user
[12490:12579:0326/193206.941401:ERROR:logging_chrome.cc(218)] Unable to create symlink /b/s/w/ite8cdBF/.org.chromium.Chromium.oemqOE/dVFm62C/test-user/chrome_debug.log pointing at /b/s/w/ite8cdBF/.org.chromium.Chromium.oemqOE/dVFm62C/test-user/chrome_debug_20180326-193206: No such file or directory (2)
[12490:12490:0326/193207.538171:WARNING:user_session_manager.cc(1068)] Attempting to save user password for non enterprise user.
[12490:12490:0326/193208.553793:ERROR:network_type_pattern.cc(134)] NetworkTypePattern: wifi: Can not match empty type.
[12490:12490:0326/193208.556500:ERROR:network_type_pattern.cc(134)] NetworkTypePattern: wifi: Can not match empty type.
[12490:12490:0326/193208.566040:ERROR:network_type_pattern.cc(134)] NetworkTypePattern: wifi: Can not match empty type.
[12490:12490:0326/193208.566949:ERROR:network_type_pattern.cc(134)] NetworkTypePattern: wifi: Can not match empty type.
../../chrome/test/views/accessibility_checker.cc:115: Failure
Failed
The following view violates DoesViewHaveAccessibilityErrors():
browser/ui/views/frame/BrowserRootView > ui/views/window/NonClientView > BrowserView > TopContainerView > ToolbarView > View > MenuButton (id 1008)
- Focusable View has no accessible name or placeholder, and the name attribute does not use kAttributeExplicitlyEmpty.
[12490:12590:0326/193211.389506:WARNING:discardable_shared_memory_manager.cc(436)] Some MojoDiscardableSharedMemoryManagerImpls are still alive. They will be leaked.
[12490:12490:0326/193211.646399:WARNING:url_request_context_getter.cc(43)] URLRequestContextGetter leaking due to no owning thread.
[  FAILED  ] ComponentToolbarActionsBrowserTest.ComponentToolbarActionsShowUpAndRespondToClicks, where TypeParam =  and GetParam() =  (6034 ms)

Looks like the culprit CL is related. Some view is violating accessibility checks that the CL added.

Assigning the author of the culprit CL, PTAL thanks!

The flakiness dashboard seems all green: https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=ComponentToolbarActionsBrowserTest.ComponentToolbarActionsShowUpAndRespondToClicks

so perhaps this fixed itself.