GitLab

This is just a couple of quick sanity checks to prevent future regressions
like the one in the linked bug. It tests both a Search+Shift shortcut and
the corresponding Prefix Key shortcut.

Adds support for sending the meta modifier key in
aura/x11 tests.

BUG=404470

Review URL: https://codereview.chromium.org/490443002

Cr-Commit-Position: refs/heads/master@{#291547}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@291547 0039d316-1c4b-4281-b951-d872f2087c98