Add a metric to record http response code for download requests.

Add a metric to record http response code for download requests.

Currently we notice an issue according to metric data that parallel
download feature has a higher SERVER_FAIL interruption type.

we would like to know more details about the http response code from
the server to analyze the cause. This metric only applies to download
requests and will also be helpful to track general download system health.

BUG=718465
Review-Url: https://codereview.chromium.org/2862743002
Cr-Commit-Position: refs/heads/master@{#469888}
(cherry picked from commit 503e20c58c8fdae480d5e7bbc538365f17e32fa1)

Review-Url: https://codereview.chromium.org/2867803002 .
Cr-Commit-Position: refs/branch-heads/3071@{#449}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed: https://chromium.googlesource.com/chromium/src/+/49b3271814acb74884e3781628c155775b7f7a0a

[xingliu, 2017-05-08 16:51:40]

Description was changed from

==========
Add a metric to record http response code for download requests.

Currently we notice an issue according to metric data that parallel
download feature has a higher SERVER_FAIL interruption type.

we would like to know more details about the http response code from
the server to analyze the cause. This metric only applies to download
requests and will also be helpful to track general download system health.

BUG=718465

Review-Url: https://codereview.chromium.org/2862743002
Cr-Commit-Position: refs/heads/master@{#469888}
(cherry picked from commit 503e20c58c8fdae480d5e7bbc538365f17e32fa1)
==========

to

==========
Add a metric to record http response code for download requests.

Currently we notice an issue according to metric data that parallel
download feature has a higher SERVER_FAIL interruption type.

we would like to know more details about the http response code from
the server to analyze the cause. This metric only applies to download
requests and will also be helpful to track general download system health.

BUG=718465

Review-Url: https://codereview.chromium.org/2862743002
Cr-Commit-Position: refs/heads/master@{#469888}
(cherry picked from commit 503e20c58c8fdae480d5e7bbc538365f17e32fa1)

Review-Url: https://codereview.chromium.org/2867803002 .
Cr-Commit-Position: refs/branch-heads/3071@{#449}
Cr-Branched-From:
a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}
Committed:
https://chromium.googlesource.com/chromium/src/+/49b3271814acb74884e3781628c1...
==========

[xingliu, 2017-05-08 16:51:42]

Committed patchset #1 (id:1) manually as
49b3271814acb74884e3781628c155775b7f7a0a.