service worker: Add UMAs for subresource response body read time

This is a follow-up CL of https://crrev.com/c/1358100. Adds
breakdown histograms for time taken reading subresource response body
by its source.

This CL also updates
ServiceWorker.LoadTiming.Subresource.ResponseReceivedToCompleted.
This was obsoleted and ResponseReceivedToCompleted2 was added
in https://crrev.com/c/1350433 but I forgot to update histograms.xml.

Change-Id: Ic9feb36ca1c10a341edb8bb73ca76afc968dbbcd
Bug: 877972
Reviewed-on: https://chromium-review.googlesource.com/c/1363732
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615330}
4 files changed