Implementors should override Repository#notifyIndexChanged(boolean)
Declare Repository#notifyIndexChanged() final and
Repository#notifyIndexChanged(boolean) abstract to force implementors
to switch to overriding the latter method. This makes Repository less
error-prone to extend since implementors no longer need to remember to
override one of those two methods.
Change-Id: I721db0f4a4865db3b35212ee0a2045d5b31c96af Signed-off-by: Jonathan Nieder <jrn@google.com>