Fix for mouse capture and release on ClearButtonElement

ClearButtonElement captures mouse events during mouse down,
and preventing 'mouseup' skips to release the mouse event capturing.

This affects mouse events on other element.
So, Removed event mousedown and mouseup handling, just changed to click. 

R=habib.virji@samsung.com
BUG=376467

Review URL: https://codereview.chromium.org/594093002

git-svn-id: svn://svn.chromium.org/blink/trunk@184076 bbb929c8-8fbe-4397-9dbb-9b2b20218538