Remove EventHandler::sendScrollEvent()

All it did was call into methods on FrameView, which was silly since
FrameView as the thing calling sendScrollEvent(). Instead move the logic
into FrameView.

Review URL: https://codereview.chromium.org/101633007

git-svn-id: svn://svn.chromium.org/blink/trunk@163655 bbb929c8-8fbe-4397-9dbb-9b2b20218538