Add histogram for webRequest listeners added with each flag

Bug: 827582
Change-Id: I86a4d5cba5901fb7430c554a4fc978789f51fb49
Reviewed-on: https://chromium-review.googlesource.com/c/1354418
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611944}
3 files changed