add missing externs to repo

externs/webextension_polyfill/urlbar/OnQueryCanceledEvent.hx

@@ -0,0 +1,18 @@
+package webextension_polyfill.urlbar;
+
+/**
+	This event is fired for the given provider when a query is canceled. The listener should stop any ongoing fetch or
+	creation of results and clean up its resources.
+**/
+typedef OnQueryCanceledEvent = {
+	/**
+		Registers an event listener <em>callback</em> to an event.
+	**/
+	function addListener(callback:(query:Query) -> Void, providerName:String):Void;
+	/**
+		Deregisters an event listener <em>callback</em> from an event.
+	**/
+	function removeListener(callback:(query:Query) -> Void):Void;
+	function hasListener(callback:(query:Query) -> Void):Bool;
+	function hasListeners():Bool;
+};