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We used to only update the command when selection changes. However, when
a folder is loaded the selection does not change, it goes from [] to []
so no event is fired. However, we do have callbacks after the folder is
populated. Use that to update the state of all the commands.

BUG=313592
R=dbeam@chromium.org

Review URL: https://codereview.chromium.org/57883004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233078 0039d316-1c4b-4281-b951-d872f2087c98