Bug 580819 - Don't try to "replace" the transient about:blank content viewer when loading about:blank immediately after it. r=smaug

docshell/base/nsDocShell.cpp

@@ -8997,6 +8997,10 @@ nsDocShell::OnNewURI(nsIURI * aURI, nsIChannel * aChannel, nsISupports* aOwner,
     PR_LOG(gDocShellLog, PR_LOG_DEBUG,
            ("  shAvailable=%i updateHistory=%i equalURI=%i\n",
             shAvailable, updateHistory, equalUri));
+
+    if (mCurrentURI && !mOSHE && aLoadType != LOAD_ERROR_PAGE) {
+        NS_ASSERTION(IsAboutBlank(mCurrentURI), "no SHEntry for a non-transient viewer?");
+    }
 #endif
 
     /* If the url to be loaded is the same as the one already there,
@@ -9006,12 +9010,18 @@ nsDocShell::OnNewURI(nsIURI * aURI, nsIChannel * aChannel, nsISupports* aOwner,
      * if this page has any frame children, it also will be handled
      * properly. see bug 83684
      *
+     * NB: If mOSHE is null but we have a current URI, then it means
+     * that we must be at the transient about:blank content viewer
+     * (asserted above) and we should let the normal load continue,
+     * since there's nothing to replace.
+     *
      * XXX Hopefully changing the loadType at this time will not hurt  
      *  anywhere. The other way to take care of sequentially repeating
      *  frameset pages is to add new methods to nsIDocShellTreeItem.
      * Hopefully I don't have to do that. 
      */
     if (equalUri &&
+        mOSHE &&
         (mLoadType == LOAD_NORMAL ||
          mLoadType == LOAD_LINK ||
          mLoadType == LOAD_STOP_CONTENT) &&