When SpdySessionPool::FindAvailableSession() is called with a new SpdySessionKey and it finds an existing SpdySession with a different key but overlapping IP address and pooling happens, it correctly logs a HTTP2_SESSION_POOL_FOUND_EXISTING_SESSION_FROM_IP_POOL type NetLog event as well as a FOUND_EXISTING_FROM_IP_POOL value in the Net.SpdySessionGet histogram.
However, it adds a new entry to |available_sessions_| with the new SpdySessionKey. Next time SpdySessionPool::FindAvailableSession() is called, LookupAvailableSessionByKey() finds the IP pooled session at [1], and the NetLog events and histogram value this time does not reflect the fact that the key is IP pooled again.
[1] https://cs.chromium.org/chromium/src/net/spdy/spdy_session_pool.cc?q=LookupAvailableSessionByKey&l=163
Comment 1 by bugdroid1@chromium.org
, Mar 10 2017