service worker: Add breakdown UMAs for response reading time of navigation

This is similar to https://crrev.com/c/1363732 but for main frame
navigation.

Bug: 877972
Change-Id: I8d2875b205aae13e36e5d2323b2b873213c80875
Reviewed-on: https://chromium-review.googlesource.com/c/1396010
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620509}
6 files changed