Fixes notification menu fade-in on swipe.

This change modifies NotificationMenuRow to fade in the menu when it
receives the onSnapOpen() callback if it hasn't start fading it in yet.
This can occur on a fast enough swipe on a non-dismissable notification,
or a fast leftward swipe on any notification with the new interruption
model enabled.

Change-Id: I4cfd01c436498d7b55e1f1f5a5584c577a699921
Fixes: 119824829
Test: manually