Commit 59f64dd

* `lazy` does not cache any of the resources up front. Instead, the Angular service worker only caches resources for which it receives requests. This is an on-demand caching mode. Resources that are never requested will not be cached. This is useful for things like images at different resolutions, so the service worker only caches the correct assets for the particular screen and orientation.

For resources already in the cache, the `updateMode` determines the caching behavior when a new version of the app is discovered. Any resources in the group that have changed since the previous version are updated in accordance with `updateMode`.

* `lazy` tells the service worker to not cache those resources. Instead, it treats them as unrequested and waits until they're requested again before updating them. An `updateMode` of `lazy` is only valid if the `installMode` is also `lazy`.

This section describes the resources to cache, broken up into three groups.

`version` provides a mechanism to indicate that the resources being cached have been updated in a backwards-incompatible way, and that the old cache entries—those from previous versions—should be discarded.

This section defines the policy by which matching requests will be cached.