Mac: Send a synthetic mouseup event when <select> popup menu is opened.

On Mac, 'mouseup' and 'click' events were not dispatched when <select> popup
menu was opened because a popup menu is opened by a mousedown event, the menu is
overlaped on the host <select>, and mouseup event is not routed to the page.
This behaivor made some compatibility problems.

We make a synthetic mouseup event in this case.  Blink core dipatches 'mosueup'
and 'click' events for it. This workaround is very similar to one in Mac Safari.

BUG=36518
R=morrita@chromium.org

Review URL: https://codereview.chromium.org/118453006

git-svn-id: svn://svn.chromium.org/blink/trunk@164215 bbb929c8-8fbe-4397-9dbb-9b2b20218538