The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/dc1f6481993e5a45bc827524bfa4cb3e5c7fc4b5

commit dc1f6481993e5a45bc827524bfa4cb3e5c7fc4b5
Author: zhongyi <zhongyi@chromium.org>
Date: Mon Apr 25 20:40:32 2016

Remove unused historgrams: Net.QuicEphemeralPortsSuggested

BUG= 603636 

Review URL: https://codereview.chromium.org/1889393002

Cr-Commit-Position: refs/heads/master@{#389554}

[modify] https://crrev.com/dc1f6481993e5a45bc827524bfa4cb3e5c7fc4b5/net/quic/quic_stream_factory.cc
[modify] https://crrev.com/dc1f6481993e5a45bc827524bfa4cb3e5c7fc4b5/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b35b415ca35f37b2c773e20f26c7a9f27ec10ada

commit b35b415ca35f37b2c773e20f26c7a9f27ec10ada
Author: zhongyi <zhongyi@chromium.org>
Date: Tue Apr 26 20:16:19 2016

Remove unused histograms: Net.QuicSession.ConnectSelectPort*

BUG= 603636 

Review URL: https://codereview.chromium.org/1895533004

Cr-Commit-Position: refs/heads/master@{#389870}

[modify] https://crrev.com/b35b415ca35f37b2c773e20f26c7a9f27ec10ada/net/quic/quic_chromium_client_session.cc
[modify] https://crrev.com/b35b415ca35f37b2c773e20f26c7a9f27ec10ada/tools/metrics/histograms/histograms.xml

Several of the listed histograms are probably reasonable to delete, but several are probably still quite useful.  Here are some comments:

Net.QuicEphemeralPortsSuggested: Feature no longer used... delete
Net.QuicSession.21*  Still very valuable for FEC design
Net.QuicSession.6*   Still very valuable for FEC design
Net.QuicSession.ConnectSelectPort*  Feature no longer used... delete
Net.QuicSession.PacketLossRate*   Probably valuable to congestion avoidance work.
Net.QuicSession.PacketReceived*   Still valuable for congestion avoidance.
Net.QuicSession.TruncatedAcksSent - Truncated acks are going away anyway.
Net.QuicSession.TruncatedAcksReceived

Thanks for the update here.

Did found out that Net.QuicSession.21* and Net.QuicSession.6* are really good data we wanna keep. I will verify the usage one by one and remove them safely. 

FYI, for any histograms that provide good data, but are not necessarily checked very regularly, you might want to add Chirp subscriptions for those histograms.

The following commit has already removed for Net.QuicSession.ConnectRandomPort
Net.QuicSession.ConnectRandomPortRequiringConfirmation:

https://chromium.googlesource.com/chromium/src/+/5830b56292abdae9c4f93c89a00edc4ad6585c41

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d74c52f2081fd4df2adb6548fe785473fccc39e0

commit d74c52f2081fd4df2adb6548fe785473fccc39e0
Author: zhongyi <zhongyi@chromium.org>
Date: Fri Aug 05 06:58:36 2016

Remove untracked histograms: Net.QuicSession.TruncatedAcksReceived/TruncatedAcksSent

BUG= 603636 

Review-Url: https://codereview.chromium.org/2217483003
Cr-Commit-Position: refs/heads/master@{#410006}

[modify] https://crrev.com/d74c52f2081fd4df2adb6548fe785473fccc39e0/net/net.gypi
[modify] https://crrev.com/d74c52f2081fd4df2adb6548fe785473fccc39e0/net/quic/chromium/quic_connection_logger.cc
[modify] https://crrev.com/d74c52f2081fd4df2adb6548fe785473fccc39e0/net/quic/chromium/quic_connection_logger.h
[delete] https://crrev.com/1209467c9a65e46ef65b3f0c4be3b1275faca676/net/quic/chromium/quic_connection_logger_unittest.cc
[modify] https://crrev.com/d74c52f2081fd4df2adb6548fe785473fccc39e0/tools/metrics/histograms/histograms.xml