Fix bug 305662: fix leakage of nsWebShell and entrained data by breaking a ref cycle between the docShell and nsISecureBrowserUI in a place that works for both embedders and the suite. r=bryner, sr=bz

git-svn-id: svn://10.0.0.236/trunk@178751 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/docshell/base/nsDocShell.cpp

@@ -3442,6 +3442,9 @@ nsDocShell::Destroy()
         mContentListener->SetParentContentListener(nsnull);
     }
 
+    // required to break ref cycle
+    mSecurityUI = nsnull;
+    
     return NS_OK;
 }