events: Add a PRESUBMIT.py script to make sure the tries run enough tests.

Changes in events can affect a number of different modules, so make sure
the unit-tests for at least ash, aura, events, keyboard, and views are
tried on the appropriate bots (linux_aura, win, win_rel, linux_chromeos,
linux_chromeos_asan).

BUG=318879
R=stip@chromium.org

Review URL: https://codereview.chromium.org/136853006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245309 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245309