merge_pr_48400

Update fetchStart in resource timing when cache is used

This CL updates fetchStart in resource timing when ServiceWorker static
routing API resource timing is used with cache as the actual source
type. This is to be compatible with other fields.

Explainer: https://github.com/WICG/service-worker-static-routing-api/blob/main/resource-timing-api.md
Bug: 41496865
Change-Id: I7c9b90f8be8cd7bef5d62edafb32b9f41448f18a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5900017
Reviewed-by: Takashi Toyoshima toyoshim@chromium.org
Reviewed-by: Yoshisato Yanagisawa yyanagisawa@chromium.org
Reviewed-by: Shunya Shishido sisidovski@chromium.org
Commit-Queue: Keita Suzuki suzukikeita@chromium.org
Cr-Commit-Position: refs/heads/main@{#1362229}