It looks like this test has been flaking a bit for quite a while (at least a week, possibly longer).

Builder: https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29

Sample flakes:
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/19614
https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/19606

Snippet of test failure output from https://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%20Tests%20%281%29/builds/19614/steps/browser_tests%20on%20Ubuntu-12.04/logs/AutomationApiTest.DesktopInitialFocus:

[10419:10419:0504/101746:INFO:CONSOLE(0)] "[FAIL] testInitialFocus: API Test Error in testInitialFocus
Actual: rootWebArea
Expected: textField
Error
    at null.<anonymous> (extensions::test:106:11)
    at null.handleRequest (extensions::binding:63:27)
    at null.<anonymous> (extensions::binding:421:32)
    at null.<anonymous> (extensions::test:213:18)
    at null.handleRequest (extensions::binding:63:27)
    at null.<anonymous> (extensions::binding:421:32)
    at chrome-extension://oldihhjalohpmjcahcebdpdhmaclbjgk/initial_focus.js:15:13
    at null.<anonymous> (extensions::automation:145:5)
    at null.handleRequest (extensions::binding:63:27)
    at null.<anonymous> (extensions::binding:421:32)", source: chrome-extension://oldihhjalohpmjcahcebdpdhmaclbjgk/initial_focus.html (0)