Use EventHandler::mouseMoved() instead of handleMouseMoveEvent().

Simplifies the code a bit since mouseMoved() also handles things
like tooltips, so WebViewImpl doesn't have to manually clear the
mouseover URL on a mouse leave.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/18147013

git-svn-id: svn://svn.chromium.org/blink/trunk@154247 bbb929c8-8fbe-4397-9dbb-9b2b20218538