The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/66f79a18126683393e20740f7d1c5646909f7e2b

commit 66f79a18126683393e20740f7d1c5646909f7e2b
Author: Karan Bhatia <karandeepb@chromium.org>
Date: Thu Jun 07 03:34:48 2018

WebRequest: Log metrics to see how often extensions don't have access to initiator.

Currently the WebRequest API only needs access to the url it intercepts. This CL
adds UMA to see the different cases pertaining to the extension's access to the
request's initiator when it has access to the requested url. This should help us
decide how extensions would be affected if the WebRequest API also started
requiring access to the request's initiator.

BUG= 836438 , 157736

Change-Id: I2fb9c5b5722382d7fed9fad3816706a99d14bde2
Reviewed-on: https://chromium-review.googlesource.com/1090036
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565166}
[modify] https://crrev.com/66f79a18126683393e20740f7d1c5646909f7e2b/extensions/browser/api/web_request/web_request_permissions.cc
[modify] https://crrev.com/66f79a18126683393e20740f7d1c5646909f7e2b/extensions/browser/api/web_request/web_request_permissions.h
[modify] https://crrev.com/66f79a18126683393e20740f7d1c5646909f7e2b/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/66f79a18126683393e20740f7d1c5646909f7e2b/tools/metrics/histograms/histograms.xml