The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0955394cb22f2b84de5a9d3a804c0f379b3455db

commit 0955394cb22f2b84de5a9d3a804c0f379b3455db
Author: asvitkine <asvitkine@chromium.org>
Date: Tue Mar 01 01:42:34 2016

Optimizations to histogram protobuf encoding.

Omits several fields from being sent if their value is one of the
common field values.

BUG= 590765 

Review URL: https://codereview.chromium.org/1744283002

Cr-Commit-Position: refs/heads/master@{#378364}

[modify] https://crrev.com/0955394cb22f2b84de5a9d3a804c0f379b3455db/components/metrics/histogram_encoder.cc
[modify] https://crrev.com/0955394cb22f2b84de5a9d3a804c0f379b3455db/components/metrics/proto/histogram_event.proto

Requesting merge to M50 - this is a very safe change that should save bandwidth for UMA users and help with the UMA for cellular launch.

Your change meets the bar and is auto-approved for M50 (branch: 2661)

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/fbb3c78c166261745387a9a6a86d42b05dcf2115

commit fbb3c78c166261745387a9a6a86d42b05dcf2115
Author: Alexei Svitkine <asvitkine@chromium.org>
Date: Wed Mar 02 18:16:05 2016

Optimizations to histogram protobuf encoding.

Omits several fields from being sent if their value is one of the
common field values.

BUG= 590765 

Review URL: https://codereview.chromium.org/1744283002

Cr-Commit-Position: refs/heads/master@{#378364}
(cherry picked from commit 0955394cb22f2b84de5a9d3a804c0f379b3455db)

Review URL: https://codereview.chromium.org/1758553004 .

Cr-Commit-Position: refs/branch-heads/2661@{#45}
Cr-Branched-From: ef6f6ae5e4c96622286b563658d5cd62a6cf1197-refs/heads/master@{#378081}

[modify] https://crrev.com/fbb3c78c166261745387a9a6a86d42b05dcf2115/components/metrics/histogram_encoder.cc
[modify] https://crrev.com/fbb3c78c166261745387a9a6a86d42b05dcf2115/components/metrics/proto/histogram_event.proto

Marking as Fixed for M50. Will file new bugs to track other improvements.