OSX CHECK() when opening new window during session restore

OSX CHECK() when opening new window during session restore

SessionRestore::RestoreSession is creating a nested message loop
and this lets in rogue dock and keyboard commands which conflict
with the restoration.
https://crash.corp.google.com/reportdetail?reportid=2137f96fd80aaf3c
https://crash.corp.google.com/reportdetail?reportid=d256ef5c849099c9
https://crash.corp.google.com/reportdetail?reportid=7c4e9e0207ab3448
https://crash.corp.google.com/reportdetail?reportid=6003f63c602bfc33

This CL explicitly checks for this session restore state and mutes
any commands during the restoration sequence.

BUG=107427
TEST=Observe crash logs.
R=mark@chromium.org

Review URL: https://codereview.chromium.org/10956023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@157848 0039d316-1c4b-4281-b951-d872f2087c98