Check for expiry dates in a 10-second window

Check for expiry dates in a 10-second window

This changes a test of expiry dates to be a 10-second range,
to account for slow testing. For example, a test may start and
set the block's expiry in one second, but by the time it is
reading the value from that block's cookie it can sometimes be
the next second. Making it 10 seconds just gives it more room
for being slow.

Bug: T153527
Change-Id: I5efde7785134a75487d31ef3d8b7b14f53b7f5d0