The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bebe5e2ef075eb28dc5a90b3c7e3db1856711072

commit bebe5e2ef075eb28dc5a90b3c7e3db1856711072
Author: jkarlin <jkarlin@chromium.org>
Date: Mon May 15 16:39:06 2017

[PageLoadMetrics] Ignore ad frames with no content

Don't report metrics on ad frames with zero bytes.

There are a few other frame count metrics that would also have to be updated
to only report frames with more than zero bytes of content. That would require
a bit more memory per frame and the metrics appear to be of limited value, so
I'm removing them. We can add them back later if we feel that we need them.

BUG= 720357 

Review-Url: https://codereview.chromium.org/2874193003
Cr-Commit-Position: refs/heads/master@{#471793}

[modify] https://crrev.com/bebe5e2ef075eb28dc5a90b3c7e3db1856711072/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.cc
[modify] https://crrev.com/bebe5e2ef075eb28dc5a90b3c7e3db1856711072/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.h
[modify] https://crrev.com/bebe5e2ef075eb28dc5a90b3c7e3db1856711072/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer_unittest.cc
[modify] https://crrev.com/bebe5e2ef075eb28dc5a90b3c7e3db1856711072/tools/metrics/histograms/histograms.xml