CL: https://codereview.chromium.org/2985573002

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

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It would be good to have this metric.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f5fc89717a49b143502d44968e42bb4f0d513033

commit f5fc89717a49b143502d44968e42bb4f0d513033
Author: Wei Li <weili@chromium.org>
Date: Mon Oct 29 21:18:11 2018

UIDevTools: Add UMA metrics to record usage

Use user action metric UI_DevTools_Connect to record each time a
connection to UI DevTools server is established. The frequency of
such connections would help us gauge the usage of the UI DevTools.

BUG= 746562 

Change-Id: Icd54da4f23b3cc0268113de48931a803af53632c
Reviewed-on: https://chromium-review.googlesource.com/c/1299007
Commit-Queue: Wei Li <weili@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603629}
[modify] https://crrev.com/f5fc89717a49b143502d44968e42bb4f0d513033/components/ui_devtools/devtools_server.cc
[modify] https://crrev.com/f5fc89717a49b143502d44968e42bb4f0d513033/tools/metrics/actions/actions.xml