Telemetry: mark session restore state as done.
This will avoid warnings from MergeSessionThrottle

BUG=321682

Review URL: https://codereview.chromium.org/94613002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237808 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237808