PWA: Use rel="preload" instead of rel="prefetch".
PWA: Use rel="preload" instead of rel="prefetch".

PiperOrigin-RevId: 189750104

chalin/angular2,chalin/angular2,angulardart/angular,matanlurey/angular,matanlurey/angular,angulardart/angular,chalin/angular2,angulardart/angular,matanlurey/angular