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Modify GetSessionIdForRestoreFromWebContents to return session id for
all browsers, because we need to save the window stack (z-order) for
all browser windows.

Modify web apps, and extension apps publishers to save app launch
information for system web apps, and platform apps, because the browser
session restore can't restore them.

For all other apps, no matter opened in tab, or window, the browser
session restore can restore them, so we don't need to save the app
launch information, we only save the browser session id as the window
id, to restore the browser windows, including window stack (z-order),
snap, etc.

The app ids for apps opened with browsers are saved as the chrome
browser's app id, because there could be multiple apps opened as tabs
in one browser, and we only need to save one browser window for them.
There will be separate CL to handle the chrome browser saving and
restoration.

BUG=1146900

Change-Id: I9f6d6675a7f7a39bd361f911d1c5cd22e898817e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2602038
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#840108}