minor refactoring

lib/frame-tree/content/frame-tree.js

@@ -28,12 +28,9 @@ this.FrameTree = (() => {
 	const TIMEOUT_INIT_REQUEST_MESSAGE = 1000;
 	const TIMEOUT_DATA_RESPONSE_MESSAGE = 1000;
 
-	const FrameTree = {
-		getFramesData
-	};
+	const FrameTree = { getFramesData };
 
-	let framesData;
-	let dataRequestCallbacks;
+	let framesData, dataRequestCallbacks;
 
 	if (window == top) {
 		browser.runtime.onMessage.addListener(message => {