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This CL adds 2 interfaces for the window management component to save
the window information, and get the saved window info based on:
go/chrome-os-full-restore-interfaces

There will be separate CLs to implement these 2 interfaces.

BUG=1146900

Change-Id: Id2885863f4e9a1725382793064e10ac7597cfb1d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2586648
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836889}