Expose workerStart in navgational service-worker fallback

Patch through the load timing info to the navigation URL loader
and use the intercepting worker's start time in the navigation
response.

Bug: 1056275
Change-Id: I53495f992d7a01bd85b2999fa3efe64b3b3e381c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4495245
Reviewed-by: Ben Kelly <wanderview@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Noam Rosenthal <nrosenthal@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1140163}

service-workers/service-worker/navigation-timing.https.html

@@ -54,6 +54,7 @@
     t.add_cleanup(() => frame.remove());
 
     const timing = await navigate_in_frame(frame, scope);
+    assert_greater_than(timing.workerStart, 0);
     verify(timing);
 }, 'Service worker controlled navigation timing network fallback');