John: I think this is simpler and will provide us with the information we need. Let's do this and leave the per-document stuff to PageLoadMetrics. Of course, the names will have changed with your recent CL.

That is, unless you've already got a solution to the other bug that you're happy with.

Okay, spoke with John. He wants to continue on  issue 851543  which frees this one up. This seems like a good one for Yao to start on.

Yao, please talk to John to familiarize yourself with what needs to be done here.

see discussion in: https://chromium-review.googlesource.com/c/1120740

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/51b414c4a62c3c556bf85b9469c857949e114e17

commit 51b414c4a62c3c556bf85b9469c857949e114e17
Author: John Delaney <johnidel@chromium.org>
Date: Tue Sep 11 15:22:28 2018

Add new per-resource metrics to AdsPageLoadMetricsObserver

Now that we have an ad flag in the browser process, log per resource
metrics for ad resource sizes. Also log new metrics for total ad bytes
per-page and for top-level ads now that this information is
available in the browser process. These metrics are different than the
existing page byte totals as they account for network bytes that went
towards canceled and incomplete resource loads.

Bug:  851543 , 859080 
Change-Id: I2ad863f0fc718f51521269d7ffd1c1bb8d0bf886
Reviewed-on: https://chromium-review.googlesource.com/1199576
Commit-Queue: John Delaney <johnidel@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590317}
[modify] https://crrev.com/51b414c4a62c3c556bf85b9469c857949e114e17/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.cc
[modify] https://crrev.com/51b414c4a62c3c556bf85b9469c857949e114e17/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.h
[modify] https://crrev.com/51b414c4a62c3c556bf85b9469c857949e114e17/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer_browsertest.cc
[modify] https://crrev.com/51b414c4a62c3c556bf85b9469c857949e114e17/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3726b2174964aabc6090dbb289bf6802af42c5c6

commit 3726b2174964aabc6090dbb289bf6802af42c5c6
Author: John Delaney <johnidel@chromium.org>
Date: Thu Oct 11 16:00:54 2018

Record Cached and Uncached resources separately in AdsPageLoadMetrics

Current resources that are cached are being reported as 0 byte
resources in Ads.ResourceUsage.Size.* histograms. This is skewing
the histograms low making it hard to see the real distribution of
resource sizes. Record cached resources in a separate histogram.

Change-Id: I379029ff70ad9f655a8e8887ff7cb5a5a3a08f5e
Bug:  859080 ,  892153 
Reviewed-on: https://chromium-review.googlesource.com/c/1258284
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: John Delaney <johnidel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598783}
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer.cc
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/chrome/browser/page_load_metrics/observers/ads_page_load_metrics_observer_browsertest.cc
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/chrome/common/page_load_metrics/page_load_metrics.mojom
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/chrome/renderer/page_load_metrics/page_resource_data_use.cc
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/chrome/renderer/page_load_metrics/page_resource_data_use.h
[modify] https://crrev.com/3726b2174964aabc6090dbb289bf6802af42c5c6/tools/metrics/histograms/histograms.xml