This refactoring removes the logic for bubbling scrolls and moves it up into EventHandler. It also removes the logicalScroll method on RenderBox and also moves that concept into EventHandler, making the scroll method in RenderBox essentially plumbing to the associated ScrollableArea. This puts most of scrolling logic in one place and makes further cleanup possible.

BUG=325554

Review URL: https://codereview.chromium.org/102983002

git-svn-id: svn://svn.chromium.org/blink/trunk@163466 bbb929c8-8fbe-4397-9dbb-9b2b20218538