[Chromedriver] Disable testShadowDomHover on HEAD

BUG=chromedriver:1503

Review-Url: https://codereview.chromium.org/2347553003
Cr-Commit-Position: refs/heads/master@{#418907}

chrome/test/chromedriver/test/run_py_tests.py

@@ -69,6 +69,8 @@ _VERSION_SPECIFIC_FILTER = {}
 _VERSION_SPECIFIC_FILTER['HEAD'] = [
     # https://code.google.com/p/chromedriver/issues/detail?id=992
     'ChromeDownloadDirTest.testDownloadDirectoryOverridesExistingPreferences',
+    # https://bugs.chromium.org/p/chromedriver/issues/detail?id=1503
+    'ChromeDriverTest.testShadowDomHover,
 ]
 
 _OS_SPECIFIC_FILTER = {}