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Major changes:
* Remove mutable reference section from Blink guide due to recent
  Google style changes.

Minor changes:
* Remove Blink guide section on documentation since the Google style
  guide already mandates this.
* Add section on TODO formatting to Dos-And-Don'ts page; remove
  similar section from Blink guide in hopes the Google guidelines +
  Dos-And-Dont's text covers it.
* Add information about C++17 (lack of) support.

Trivial changes:
* Clarify that the Blink style guide is a diff atop the Chromium
  guide (which is a diff atop the Google guide).
* Cite Chromium guidance around bare "new" from Blink guide.
* Minor link fixes, wording changes, inlining.

Bug: none
Change-Id: I1e3c2b265930cc73501e3557b25ca52b6902126e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2223452
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774352}