Workaround for VS 2005 bug with inheritance from nested classes.

BUG=http://crbug.com/61717
TEST=Build on VS 2005
Review URL: http://codereview.chromium.org/4271003


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@64939 0039d316-1c4b-4281-b951-d872f2087c98