Properly redispatch systemUiVisibility flags

Fixes two bugs introduced by change
I7bd32531130d199c0734ffcb800194e77b7e16c3:

When the system window insets consumed by DecorView
change as a result of changing flags, the insets must
be redispatched to the hierarchy.

Also fixes a bug where, as a result of removing the wrong
implication of the SYSTEM_UI_FLAG_LAYOUT_STABLE flag by
FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS, the status bar was
being forced to black when returning from recents.

Bug: 17489047
Bug: 15046646
Change-Id: I127b0ff3b17c4873a7c28d67020f84298ed09db2