Disable ChromeDriverTest.testHasFocusOnStartup

Very flaky on Mac 10.10 Tests.

Bug: chromium:868376
Change-Id: I415dd89ba7c666630e2d65950c2c5472d2e11968
Reviewed-on: https://chromium-review.googlesource.com/1155819Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579221}

chrome/test/chromedriver/test/run_py_tests.py

@@ -113,6 +113,8 @@ _OS_SPECIFIC_FILTER['mac'] = [
     'ChromeDriverTest.testWindowMinimize',
     # https://bugs.chromium.org/p/chromedriver/issues/detail?id=2522
     'ChromeDriverTest.testWindowMaximize',
+    # https://bugs.chromium.org/p/chromium/issues/detail?id=868376
+    'ChromeDriverTest.testHasFocusOnStartup',
 ]
 
 _DESKTOP_NEGATIVE_FILTER = [