Stop relying on WillSendRequest and DidReceiveResponse callbacks for main resource

WillSendRequest for main resource happens during BeginNavigation, so we can just
skip it during commit time.

The logic of saving metrics from DidReceiveResponse has been copied to CommitNavigation.
We could get rid of DidReceiveResponse entirely if we were always going through
CommitNavigation path, but we sometimes don't (see kWebNavigationPolicyCurrentTab
returned from RFI::DecidePolicyForNavigation).

Bug: 855189
Change-Id: Ib78bda6e22e4a301adf7c66215568ca6f02fa01d
Reviewed-on: https://chromium-review.googlesource.com/1145900
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578783}
2 files changed