Don't crash when closing interstitial pages.

content/browser/frame_host/interstitial_page_impl.h

Index: content/browser/frame_host/interstitial_page_impl.h
diff --git a/content/browser/frame_host/interstitial_page_impl.h b/content/browser/frame_host/interstitial_page_impl.h
index e0e0ff5c9730a16c07f719b65e20813d5e4150ce..cc9dc63b5ebe3455e34820fc918fcc64a5082da9 100644
--- a/content/browser/frame_host/interstitial_page_impl.h
+++ b/content/browser/frame_host/interstitial_page_impl.h
@@ -69,6 +69,10 @@ class CONTENT_EXPORT InterstitialPageImpl
   virtual void SetSize(const gfx::Size& size) OVERRIDE;
   virtual void Focus() OVERRIDE;
 
+  // This is called by a hosting WebContents to notify this interstitial page
+  // that it is going away.
+  void WebContentsWillBeDestroyed();
+
   // Allows the user to navigate away by disabling the interstitial, canceling
   // the pending request, and unblocking the hidden renderer.  The interstitial
   // will stay visible until the navigation completes.