Summarizing discussion with zhongyi@: We can limit the connection close on IpAddressChange notification to some Android platforms, to avoid aggressively closing on desktop.

The plan is to close connections only on platforms where NetworkHandles are supported (Android >= L). This avoids the most recent internal issue on Android version O, and also avoids being aggressive on desktop.

My recollection is that we ran a field trial for this and did not see problems with metrics and intended to turn it on by default. Do we now think that analysis was incorrect?

I think I had a clue: default on close session on ip address change is the one caused the spike.

Before turning on this feature by default, platforms will not receive OnIPAddressChange notification as IPAddressObserver is not registered.

When we default on this feature, we register the IPAddressObserver on all platforms, including the desktop. Thus desktop is also closing sessions OnIpAdressChanged. 

This can be tracked on histogram as Net.QuicSession.PlatformNotification[NETWORK_IP_ADDRESS_CHANGED] is close to Net.QuicSession.ConnectionCloseErrorCodeClient[IP_ADDRESS_CHANGED].

*Linux: https://uma.googleplex.com/p/chrome/histograms/?endDate=20171008&dayCount=1&histograms=Net.QuicSession.ConnectionCloseErrorCodeClient%2CNet.QuicSession.PlatformNotification&fixupData=true&showMax=true&filters=platform%2Ceq%2CL%2Cchannel%2Ceq%2C2%2Cmilestone%2Cge%2C61%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial
*Android: https://uma.googleplex.com/p/chrome/histograms/?endDate=20171008&dayCount=1&histograms=Net.QuicSession.ConnectionCloseErrorCodeClient%2CNet.QuicSession.PlatformNotification&fixupData=true&showMax=true&filters=platform%2Ceq%2CA%2Cchannel%2Ceq%2C2%2Cmilestone%2Cge%2C61%2Cisofficial%2Ceq%2CTrue&implicitFilters=isofficial

jri@: have we experimented this feature on desktop before? 

On, this experiment is default on Stable channel. And Dev channel doesn't have this experiment. That's why dev channel witnessed a bump from 0% to 1%.

This experiment is default on for 76% users on Stable before 9/19, looking at stable histograms, this error code proportion is around 1.4% on desktop (https://uma.googleplex.com/timeline_v2?sid=d24c6e3eaece966c3af167a6eaaeb47b)

We would expect this to increase around 2% if 63.0.3222.0 rolls out to Stable. Current dev channel are seeing this error rate around 1%, which is within expectation. (https://uma.googleplex.com/timeline_v2?sid=60899bed88048f9c4bfcd48e96200c12)

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