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Migrate the Developer Settings page from deprecated Framework
preferences to the Preferences Support Library.

This is the first fragment migrated that includes a ChromeBasePreference
so some base classes and methods have been duplicated here to support
simultaneous compatibility between Framework and Support Library
Preferences.

Bug: 966244
Change-Id: I2bd8919361207576231f99d799a5a7e95819d81e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632557
Commit-Queue: Natalie Chouinard <chouinard@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666356}