Attempting to De-flake resource loading browsertests

I've made the callback more in line with the specific update. I suspect
that the problem is other hints are being fed in slightly earlier than
the update from the tests. This makes sure the callback is tied to the
correct update.

Bug: 932913
Change-Id: I5f23a5321a555c925e29b9e08d50ab99afdeb5bf
Reviewed-on: https://chromium-review.googlesource.com/c/1484087
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Reviewed-by: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634917}
5 files changed