Don't require two-pass updateScrollbars for overlay scrollbars
Don't require two-pass updateScrollbars for overlay scrollbars

The original logic of updateScrollbars requires two passes if any scrollbar
disappears, and r148574 broke that for overlay scrollbars. Disable the logic
that requires two passes for overlay scrollbars.

BUG=231698

Review URL: https://chromiumcodereview.appspot.com/13998029

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@148691 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs