Add Printing.CUPS.PrintersDiscovered to our metrics.

Add Printing.CUPS.PrintersDiscovered to our metrics.

In order to understand how many printers users are seeing in the
discovered printers dialog, track it using UMA.  The metric is recorded
when the discoverer declares scanning to be complete.

BUG=726819
Review-Url: https://codereview.chromium.org/2904243003
Cr-Original-Commit-Position: refs/heads/master@{#475649}
Review-Url: https://codereview.chromium.org/2926653003 .
Cr-Commit-Position: refs/branch-heads/3112@{#207}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed: https://chromium.googlesource.com/chromium/src/+/c86d7012ddedff5dd300906c9ec1ce9bccc9aae3

[skau, 2017-06-06 21:13:23]

Description was changed from

==========
Add Printing.CUPS.PrintersDiscovered to our metrics.

In order to understand how many printers users are seeing in the
discovered printers dialog, track it using UMA.  The metric is recorded
when the discoverer declares scanning to be complete.

BUG=726819

Review-Url: https://codereview.chromium.org/2904243003
Cr-Commit-Position: refs/heads/master@{#475649}
(cherry picked from commit fc8c7f3440cecb52667340276ea06100e303d4df)
==========

to

==========
Add Printing.CUPS.PrintersDiscovered to our metrics.

In order to understand how many printers users are seeing in the
discovered printers dialog, track it using UMA.  The metric is recorded
when the discoverer declares scanning to be complete.

BUG=726819

Review-Url: https://codereview.chromium.org/2904243003
Cr-Original-Commit-Position: refs/heads/master@{#475649}
Review-Url: https://codereview.chromium.org/2926653003 .
Cr-Commit-Position: refs/branch-heads/3112@{#207}
Cr-Branched-From:
b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed:
https://chromium.googlesource.com/chromium/src/+/c86d7012ddedff5dd300906c9ec1...
==========

[skau, 2017-06-06 21:13:24]

Committed patchset #1 (id:1) manually as
c86d7012ddedff5dd300906c9ec1ce9bccc9aae3.