init/instance: fix NW.js window initialization

Resolves #911

Don't call `requestAnimationFrame` while the application window is still
hidden during initialization. NW.js sometimes doesn't execute the
animation frame callback during the initial window visibility state.
This became clear after the NW.js 0.68.1 upgrade recently, which lead to
the initialization never completing in certain cases on some systems.

Remove the two `requestAnimationFrame` calls and schedule the
`afterRender` Ember run-loop callback in the next run-loop, which
ensures that the DOM is actually fully loaded and rendered by NW.js, so
that no white screen appears for a few frames, which needs to be avoided
when using the dark theme.

Author: bastimeyer

src/app/init/instance-initializers/nwjs/instance-initializer.js

@@ -1,6 +1,6 @@
 import { get } from "@ember/object";
 import { addObserver } from "@ember/object/observers";
-import { scheduleOnce } from "@ember/runloop";
+import { later, scheduleOnce } from "@ember/runloop";
 import { default as nwApp, quit } from "nwjs/App";
 import { default as nwWindow, setVisibility, setFocused } from "nwjs/Window";
 import { argv, parseCommand } from "nwjs/argv";
@@ -52,12 +52,11 @@ export default {
 			// restore window position first (while being hidden)
 			await windowInitializer( application );
 
-			// wait until Ember has rendered the app for the first time (window is still hidden)
-			await new Promise( resolve => scheduleOnce( "afterRender", resolve ) );
-			// assume that NW.js doesn't render a white page anymore after the next two frames
-			for ( let i = 0; i < 2; i++ ) {
-				await new Promise( resolve => requestAnimationFrame( resolve ) );
-			}
+			// Wait until Ember has rendered the app for the first time (window is still hidden).
+			// Wrap scheduled "afterRender" run-loop queue callback in a new run-loop to ensure
+			// that the DOM is fully rendered and no white screen will appear for a few frames.
+			// We can't use requestAnimationFrame here due to issue #911.
+			await new Promise( resolve => later( () => scheduleOnce( "afterRender", resolve ) ) );
 
 			// wait until the target route is loaded
 			const routeName = await routingPromise;