In this case it is simulating iOS and Android GUI "pixel by pixel"
by using Skia graphics engine of Chrome and Dart programming language. Very clever.
Skia is also used by Xamarin for portable graphics,
and could be used by .NET Core as substitute for WinForms.
So technically this could be alternative for Java on Android.
And all this "pain" is just to avoid using simple mobile-ready portable Web.
There is clearly a need for a better "web", with concept of "portable apps".
Xamarin, React native, NativeScript, Appcelerator Titanium...
Dart News: Angular 2 Dart and Flutter @ InfoQ
"Flutter is Google’s tool for writing cross-platform applications for Android and iOS in Dart. With a single codebase developers can target both mobile platforms. Unlike other tools, Flutter does not rely on native rendering but it uses the Skia graphics engine, also used by Android, Chrome and Firefox, to mimic the native interface including fonts and hand gestures.
A key benefit of using Flutter is its extremely fast development cycle, thanks to the Dart VM and Flutter's functional-reactive framework. For both iOS and Android, hardware and emulators, developers using Flutter can experience sub-second dev cycles as they add and debug app UIs. The app's state is maintained during the reloads, which means developers can iterate very quickly without restarting their app for every change"
"Dart has seen major support within Google, two of their most important products, AdSense and AdWords being built with it"