The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a875acbbe399a1803b334c77b947f943822edf6e

commit a875acbbe399a1803b334c77b947f943822edf6e
Author: Ben Kelly <wanderview@chromium.org>
Date: Fri Sep 21 19:31:34 2018

Measure mojo::DataPipe creation time on the ServiceWorker thread.

We've seen some anecdotal evidence in local testing that mojo::DataPipe
creation can sometimes take milliseconds to complete.  Currently there
is a pipe created on the ServiceWorker thread for certain FetchEvent
respondWith() code paths.  This histogram will help us determine if
this is introducing jank on the service worker thread.

Bug:  888045 
Change-Id: I5f36da2dfbde4bd561c605336949e475f45ecb43
Reviewed-on: https://chromium-review.googlesource.com/1239274
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593302}
[modify] https://crrev.com/a875acbbe399a1803b334c77b947f943822edf6e/third_party/blink/renderer/modules/service_worker/fetch_respond_with_observer.cc
[modify] https://crrev.com/a875acbbe399a1803b334c77b947f943822edf6e/tools/metrics/histograms/histograms.xml