Issue #2452 - Bail out from PresShell::Initialize if the pres shell is being destroyed in XBLConstructorRunner

https://bugzilla.mozilla.org/show_bug.cgi?id=1428694

layout/base/nsPresShell.cpp

@@ -1771,6 +1771,9 @@ PresShell::Initialize(nscoord aWidth, nscoord aHeight)
     // (Do this in a script runner, since our caller might have a script
     // blocker on the stack.)
     nsContentUtils::AddScriptRunner(new XBLConstructorRunner(mDocument));
+
+    // XBLConstructorRunner might destroy us.
+    NS_ENSURE_STATE(!mHaveShutDown);
   }
 
   NS_ASSERTION(rootFrame, "How did that happen?");