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This CL adds FullRestoreSavehandler class and the SaveAppLaunchInfo
interface to prepare for the restore data writing implementation.

There will be separate CL to implement the restore data and the
FullRestoreFileHandler class to  run the actual writing with a
background task runner.

BUG=1146900

Change-Id: I2ff73b40d6441e0f581b7f4a5b035cf6156241c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2580922
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836560}