add missing externs to repo

externs/webextension_polyfill/proxy/Static.hx

@@ -0,0 +1,16 @@
+package webextension_polyfill.proxy;
+
+typedef Static = {
+	/**
+		Fired when proxy data is needed for a request.
+	**/
+	var onRequest : OnRequestEvent;
+	/**
+		Notifies about errors caused by the invalid use of the proxy API.
+	**/
+	var onError : webextension_polyfill.events.Event<(error:OnErrorErrorType) -> Void>;
+	/**
+		Configures proxy settings. This setting's value is an object of type ProxyConfig.
+	**/
+	var settings : webextension_polyfill.types.Setting;
+};