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This is the preparing for the full restore file reading function. Add
the construct function for RestoreData to convert the JSON format to
the RestoreData.

Add the unit tests to verify the convert function:
RestoreData -> base::Value -> RestoreData.

BUG=1146900

Change-Id: I54133e83e9b7abce62c5812cc5e87941e770f958
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2591987Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837465}