Ignore overflow:hidden in overview mode.

The feature was enabled to prevent flash sites from flickering due to
viewport height change when the site is scrolled.

Now fixed viewport height is in honeycomb, this flickering shall be
a non-issue.  So to support better scrolling of overflow:hidden sites
and better consistency, overflow:hidden in overview mode is ignored
as well.

Tested on flash site http://home.disney.go.com/mwc.index to make sure
no flickering happens.  More testing shall be done once good flash
player is there.

issue: 3330038
Change-Id: Ia3f61ce49cfb970d26976d4e876c337d210a9df2