queue event instead of immediately fire

created checks to see if parser is in use before event dispatch

changed tests to expect crash and added async style test

components/script/dom/document.rs

@@ -1885,6 +1885,13 @@ impl Document {
         self.current_parser.get()
     }
 
+    pub fn can_invoke_script(&self) -> bool {
+        match self.get_current_parser() {
+            Some(parser) => parser.parser_is_not_active(),
+            None => true,
+        }
+    }
+
     /// Iterate over all iframes in the document.
     pub fn iter_iframes(&self) -> impl Iterator<Item=DomRoot<HTMLIFrameElement>> {
         self.upcast::<Node>()