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+ adds a wrapper around defaults and makes this a singleton.
+ Creates a new settings object to save settings in.
+ Serializes the settings to and from defaults.

Change-Id: I8e4aaed4c38fd02ca8a71b410c6d441e17da72b6
Reviewed-on: https://chromium-review.googlesource.com/574888
Commit-Queue: Scott Nichols <nicholss@chromium.org>
Reviewed-by: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487308}