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There is already an ash::GetRootWindowController, and it does the same thing.

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/10828037

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148662 0039d316-1c4b-4281-b951-d872f2087c98