The sheriff link isn't stable. But the flakiness Dashboard confirms the flakiness:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=chromedriver_py_tests&tests=testTakeElementScreenshot

As it's assigned, remove from sheriff queue.

Taking a look...

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5be06c19e55ed417456b503df4e0b518ce53c310

commit 5be06c19e55ed417456b503df4e0b518ce53c310
Author: Yuri Wiitala <miu@chromium.org>
Date: Tue Dec 18 02:07:29 2018

Disable ChromeDriverTest.testTakeElementScreenshot on Mac10.10.

When pixel comparison fails on Mac OS X 10.10 (no other version), log an
error message and allow a "free pass." This effectively is the same as
disabling the test for just this specific Mac version.

Bug:  913603 
Change-Id: Ifc7b30a12d26d4f61059bd7da169543f6ce0209d
Reviewed-on: https://chromium-review.googlesource.com/c/1380946
Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617344}
[modify] https://crrev.com/5be06c19e55ed417456b503df4e0b518ce53c310/chrome/test/chromedriver/test/run_py_tests.py

 Issue 897222  has been merged into this issue.

 Bug 897222  has attached graphics files that show the likely root cause of this bug. It seems, in a small number of test runs, the RHS vertical scrollbar is being captured in the image.

In any case, the change in comment 3 has resolved the issue. Things have been consistently green for a while on the flakiness dashboard.