Update arrow color after all notifications dismissed.

assignMarginsAndBackgrounds updates determines the new arrow color, but
it doesn't actually update it. That is normally done in
updateArrowColor.

Test: Icon menu arrow color changes to content above it after notification
dots dismissed.
Fix: 201458705

Change-Id: I5ee40b420b03c29c197983af5968d4f2902bc59b
2 files changed