Use FileNetLogObserver in the net-internals browser_tests.

Bug: 716570
Change-Id: I9a81dff8ed17ff9d61b89c9ef887a918770a80a9
Reviewed-on: https://chromium-review.googlesource.com/563862
Reviewed-by: Matt Menke <mmenke@chromium.org>
Commit-Queue: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#485386}
3 files changed