Attach QuicAckNotifiers to the serialized packet, instead of individual

Attach QuicAckNotifiers to the serialized packet, instead of individual
stream frames.

Protected behind FLAGS_quic_attach_ack_notifiers_to_packets.

A call to QuicPacketGenerator::ConsumeData may result in multiple stream
frames, in multiple packets, being created to hold the data. Previously
the QuicAckNotifier was attached to each *frame*, but really it should
be attached to the serialized *packet* as the notifier is interested in
knowing when the *packet* gets ACKed.

No behavior change intended.

Added an end to end test demonstrating that the AckNotifier works in the
face of 30% packet loss. Earlier rch and I were sceptical this refactor
would work with retransmissions, but the QuicAckNotifierManager still
recieves calls to UpdateSequenceNumber and does the right thing.

Merge internal change: 83452063

R=rch@chromium.org

[ramant (doing other things), 2015-01-10 01:15:47]

Patchset #2 (id:20001) has been deleted

[Ryan Hamilton, 2015-01-10 01:24:19]

lgtm