The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9c76cfaf64b27534abe2663b2a1768737d64d4f9

commit 9c76cfaf64b27534abe2663b2a1768737d64d4f9
Author: mek <mek@chromium.org>
Date: Sun Nov 20 03:59:06 2016

Add a use counter for Link rel=serviceworker headers.

Even though these link headers aren't processed in blink, this is still
the most sensible place for a use counter for these.

BUG= 582310 , 667086 

Review-Url: https://codereview.chromium.org/2513183002
Cr-Commit-Position: refs/heads/master@{#433444}

[modify] https://crrev.com/9c76cfaf64b27534abe2663b2a1768737d64d4f9/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/9c76cfaf64b27534abe2663b2a1768737d64d4f9/third_party/WebKit/Source/core/loader/LinkLoader.cpp
[modify] https://crrev.com/9c76cfaf64b27534abe2663b2a1768737d64d4f9/tools/metrics/histograms/histograms.xml

I'd like to backport this use counter to M56

Your change meets the bar and is auto-approved for M56 (branch: 2924)

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This was merged to 2924, not sure why bugdroid didn't update the issue.