Log printer additions and removals by protocol.

Log printer additions and removals by protocol.

In order to track printer churn, we record an event when a printer is
succesfully added and when a printer is removed in the settings dialogs.
This data is tracked by protocol.

BUG=726103
Review-Url: https://codereview.chromium.org/2903883003
Cr-Original-Commit-Position: refs/heads/master@{#476146}
Review-Url: https://codereview.chromium.org/2923893002 .
Cr-Commit-Position: refs/branch-heads/3112@{#210}
Cr-Branched-From: b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed: https://chromium.googlesource.com/chromium/src/+/11389fcea63dd43c32a78a9cc2342e82cdff598c

[skau, 2017-06-06 21:18:36]

Description was changed from

==========
Log printer additions and removals by protocol.

In order to track printer churn, we record an event when a printer is
succesfully added and when a printer is removed in the settings dialogs.
This data is tracked by protocol.

BUG=726103

Review-Url: https://codereview.chromium.org/2903883003
Cr-Commit-Position: refs/heads/master@{#476146}
(cherry picked from commit 6d46ea6e7636ecdb53b00795f4893cbc32694f30)
==========

to

==========
Log printer additions and removals by protocol.

In order to track printer churn, we record an event when a printer is
succesfully added and when a printer is removed in the settings dialogs.
This data is tracked by protocol.

BUG=726103

Review-Url: https://codereview.chromium.org/2903883003
Cr-Original-Commit-Position: refs/heads/master@{#476146}
Review-Url: https://codereview.chromium.org/2923893002 .
Cr-Commit-Position: refs/branch-heads/3112@{#210}
Cr-Branched-From:
b6460e24cf59f429d69de255538d0fc7a425ccf9-refs/heads/master@{#474897}
Committed:
https://chromium.googlesource.com/chromium/src/+/11389fcea63dd43c32a78a9cc234...
==========

[skau, 2017-06-06 21:18:37]

Committed patchset #1 (id:1) manually as
11389fcea63dd43c32a78a9cc2342e82cdff598c.