Support macOS text substitutions.

Web content now performs substitutions as configured in System
Preferences → Keyboard → Text, including quotes, dashes, and custom
replacements.

To do:
- Add standard Edit menu options (see TextEdit).
- Maybe: tweak about how substitutions work with undo.
- Maybe: support reverting and changing suggestions via the standard UI.
- Maybe: offer automatic spelling and grammar correction.
- Probably: more! This is just a first pass.

Bug: 42434
Change-Id: I35ed072a9a390296f9ab250c788e11b9147dc24b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1652661
Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Sidney San Martín <sdy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#670139}
6 files changed