Update Handle Fetch to return timing info (#1772)
This change ensures that timing information is propagated to the caller even when a network fallback occurs. Consequently, Service Worker timing information can now be configured as outlined in the explainer, once related specifications are updated to support this behavior.
https://github.com/WICG/service-worker-static-routing-api/blob/main/resource-timing-api.md#correspondence-of-the-matched-source-type-and-the-actual-source-type
