Timeout autoHide notifications based on visible time

Timeout autoHide notifications based on visible time

On supported browsers handle the auto hide timeout with a
count of cumulative time the page has been visible to the
user. Old functionality can still be accessed, if desired,
by setting the visibleTimeout notification option to false.
On browsers without support for this visibilitychange event
wall clock time (the old behaviour) is used.

Adds a library function functionally similar to setTimeout that
only considers time when the page is visible. This is useful
both for analytics purposes, and when you want to temporarily
put something on screen and be reasonably certain it doesn't
go away until a user has seen it.

Bug: T42322
Change-Id: I7d8ea85602cae9cfc72e0155bc3092049ecafd43