When talking >=QUIC_VERSION_22, regularly send updated bandwidth

When talking >=QUIC_VERSION_22, regularly send updated bandwidth
estimates to the client (in SCUP messages).

The main work is in QuicConnection, where a new alarm regularly checks
for substantially changed bandwidth estimates and sends them to the
client if so. The majority of the rest of this CL is plumbing, and test
code.

Feel free to suggest better values for:
- Timeout between bandwidth estimate alarms
- Definition of "substantial change" in estimate

The flow is:

- on every congestion event (ACK, packet loss) the sent packet manager
  passes a bandwidth estimate to the sustained bandwidth recorder
- on every congestion window change, the QuicServerSession checks to see
  if the bandwidth has changed sufficiently *and* enough time has passed
  since last time we sent an update to the client
- if so, it populates the CachedNetworkParams proto, and passes this to
  the CryptoStream which sends a SCUP message to the client

Merge internal change: 73579021

R=rch@chromium.org, rjshade@chromium.org, wtc@chromium.org

[ramant (doing other things), 2014-08-21 17:02:31]

https://codereview.chromium.org/490263003/diff/1/net/tools/quic/quic_server_s...
File net/tools/quic/quic_server_session_test.cc (right):

https://codereview.chromium.org/490263003/diff/1/net/tools/quic/quic_server_s...
net/tools/quic/quic_server_session_test.cc:101: MATCHER_P(EqualsProto,
network_params, "") {
Hi Ryan,
  Implemented EqualsProto to compare every member of CachedNetworkParameters.
This is used in tests only. Should we add Equals (or == operator) method in
CachedNetworkParameters class?

thanks
raman

[wtc, 2014-08-21 22:10:19]

Patch set 1 LGTM. I only skimmed over the CL, so please consider this a drive-by
review.

[Ryan Hamilton, 2014-08-21 22:11:36]

lgtm

https://codereview.chromium.org/490263003/diff/1/net/tools/quic/quic_server_s...
File net/tools/quic/quic_server_session_test.cc (right):

https://codereview.chromium.org/490263003/diff/1/net/tools/quic/quic_server_s...
net/tools/quic/quic_server_session_test.cc:101: MATCHER_P(EqualsProto,
network_params, "") {
On 2014/08/21 17:02:31, ramant wrote:
> Hi Ryan,
>   Implemented EqualsProto to compare every member of CachedNetworkParameters.
> This is used in tests only. Should we add Equals (or == operator) method in
> CachedNetworkParameters class?
> 
> thanks
> raman

As discussed offline, this SGTM.