This will allow us to schedule these timers differently in the future.
This patch only performs the refactoring, and is not intended to change
any behavior. Specifically, this patch doesn't change the order in
which timeouts are fired -- they should still all be fired according to
the mWhen field.
The implementation works by splitting timeout storage per window into
two Timeouts objects, mNormalTimeouts and mTrackingTimeouts. The ForEach
helper methods are extended to deal with both of these objects, and as a
result, most of the algorithms operating on the list of timeouts work
correctly without any modification, with the notable exception of
RunTimeout.
In RunTimeout(), the order in which Timeout objects are processed does
matter, so for that case we use the OrderedTimeoutIterator class to
iterate over both linked lists simultaneously in the mWhen order. Also,
inserting the dummy timeout when running the timeouts is only necessary
for the linked list where the last expired timeout is coming from, so we
only inject the dummy timer into the corresponding list, therefore we
remember which list we picked the last expired timeout from when
looking for it.
Ben Kelly
Ehsan Akhgari