Fix a crasher in the interstitial pages

A crasher would happen if you navigate to a page triggering an interstitial from the new tab page, then press back in the interstitial.
The crasher would happen because the navigation controller collects (destroys) the previous tab contents when a navigation is initiated. In this case, when navigating back (by just discarding the non committed entries), it would not be expect that the tab contents would be NULL.

It seems we do not need to collect the unused tab contents on NavigateToPendingEntry() since we are collecting any unused TabContents in NavigationController::RendererDidNavigate().

BUG=6408
TEST=From the new page, enter the URL to a malware site (ex: http://ianfette.org), press Back (or close the tab), there should be no crash.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=8350

[brettw, 2009-01-20 23:38:13]

LGTM