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* Make ui/views/.clang-tidy additive to the base file, not a
  replacement.
* Hoist the "use equals" config option to the base file, since that's
  Chromium style.
* Update docs for errors or inclarities.

Bug: none
Change-Id: I7f22db99d9ff11fc91665776887a02f7184427ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2483344
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: George Burgess <gbiv@chromium.org>
Reviewed-by: George Burgess <gbiv@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818330}