First-cut at fixing unhandled Tap event returns in Blink.

We want to be able to recognize tap events that the page has not handled and provide some useful default behavior for those events.  Currently taps are considered handled in many cases when they really have not been handled by the page or default behavior.  This CL is a beginning at correcting this.  We plan to also check if the tap interacted with an element with an ARIA role that indicates it was interactive.

BUG=355154

Review URL: https://codereview.chromium.org/267313008

git-svn-id: svn://svn.chromium.org/blink/trunk@175514 bbb929c8-8fbe-4397-9dbb-9b2b20218538