Fixing a timing ordering bug for main frame fetch timing in DRP

This CL addresses an event ordering bug that affects DRP pingbacks.
Specifically, OnCommit in PLM and OnResourceLoaded for the main frame
resource do not have a defined ordering, so this assumption should not
be made by any parts of the code.

Bug: 916333
Change-Id: I299ed008beccf5b5ae4cce16df233bd8a132a789
Reviewed-on: https://chromium-review.googlesource.com/c/1383536
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617964}
5 files changed