New Route.setCatchHandler() method

[jeffposnick]

Library Affected:
workbox-routing

I was thinking that we should add in a Route-level setCatchHandler() method, which would behave like the existing Router.setCatchHandler(), but instead of being a global to the Router instance, it would apply only when there's an exception throw by the HandlerCallback associated with the specific Route.

Something like:

const navigationRoute = new NavigationRoute(new NetworkOnly());

// Everything that extends Route would support setCatchHandler():
navigationRoute.setCatchHandler((routeHandlerCallbackParams) => {
  return caches.match('/offline.html');
  // Or do something using routeHandlerCallbackParams to create a Response
});

registerRoute(navigationRoute);

This would be post-v5, as it should be backwards-compatible.

[Snugug]

Run route's catch handler, fall back to global if route's CH throws (if one exists)