Disable ChromeDriverTest.testShadowDomFindElement on Mac

Tbr: shengfa@google.com
No-try: true
Bug: 1157533
Change-Id: I21d98df4d1062a133c895452c1632120001e5446
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2587234Reviewed-by: Ella Ge <eirage@chromium.org>
Commit-Queue: Ella Ge <eirage@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836157}

chrome/test/chromedriver/test/run_py_tests.py

@@ -106,6 +106,8 @@ _OS_SPECIFIC_FILTER['mac'] = [
     'ChromeDriverTest.testActionsMultiTouchPoint',
     # Flaky: https://crbug.com/1156576.
     'ChromeDriverTestLegacy.testContextMenuEventFired',
+    # Flaky: https://crbug.com/1157533.
+    'ChromeDriverTest.testShadowDomFindElement',
 ]
 
 _DESKTOP_NEGATIVE_FILTER = [