Bug 834732 - Assert proper cx stack handling in WrapperFactory::Rewrap. r=mrbkap

js/xpconnect/src/XPCWrappedJSClass.cpp

@@ -492,6 +492,7 @@ nsXPCWrappedJSClass::IsWrappedJS(nsISupports* aPtr)
            result == WrappedJSIdentity::GetSingleton();
 }
 
+// NB: This returns null unless there's nothing on the JSContext stack.
 static JSContext *
 GetContextFromObject(JSObject *obj)
 {

js/xpconnect/wrappers/WrapperFactory.cpp

@@ -341,6 +341,9 @@ WrapperFactory::Rewrap(JSContext *cx, JSObject *existing, JSObject *obj,
                "wrapped object passed to rewrap");
     MOZ_ASSERT(JS_GetClass(obj) != &XrayUtils::HolderClass, "trying to wrap a holder");
     MOZ_ASSERT(!js::IsInnerObject(obj));
+    // We sometimes end up here after nsContentUtils has been shut down but before
+    // XPConnect has been shut down, so check the context stack the roundabout way.
+    MOZ_ASSERT(XPCJSRuntime::Get()->GetJSContextStack()->Peek() == cx);
 
     // Compute the information we need to select the right wrapper.
     JSCompartment *origin = js::GetObjectCompartment(obj);