Fix ChromeOS webui GAIA login crash.
Fix ChromeOS webui GAIA login crash.

AutoLoginInfoBarDelegate uses TabContentsWrapper which is NULL for
TabContents hosted in HTMLDialog.

BUG=chromium-os:17711
TEST=Verify fix for chromium-os:17711


Review URL: http://codereview.chromium.org/7401023

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@92959 0039d316-1c4b-4281-b951-d872f2087c98

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