The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3

commit ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3
Author: Dale Curtis <dalecurtis@chromium.org>
Date: Wed Dec 06 23:28:10 2017

Update WatchTimeReporter to report bg audio, video, bg video.

Today WTR doesn't report background audio nor anything for video
only streams; this change populate UKM with this data.

Additionally, audio background data is reported to UMA (because
otherwise we'd just lose a large chunk of what we report today),
while video only data is just reported to UKM for now. Video only
can be enabled later by simply adding the histograms.xml entries
and updating the filter in WatchTimeRecorder.

All of this is done by essentially removing all restrictions from
WatchTimeReporter. We now always construct a background reporter
and we always report shown/hidden status regardless of audio/video
presence.

This will cause a large drop off in Audio listen time since all
background time will go into a new background bucket now. While the
two metrics should sum to close to the same value, some loss is
expected until http://crbug.com/779192 is fixed to roll-up
unreported watch time for transition states.

BUG= 775731 , 775685 , 775681 
TEST=expanded existing tests to cover all functionality.

Change-Id: I55eb69b074d00750b5bd9ed47585380f92c882ca
Reviewed-on: https://chromium-review.googlesource.com/809620
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522246}
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/base/watch_time_keys.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/base/watch_time_keys.h
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/blink/watch_time_reporter.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/blink/watch_time_reporter.h
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/blink/watch_time_reporter_unittest.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/blink/webmediaplayer_impl.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/mojo/interfaces/watch_time_recorder.mojom
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/mojo/services/watch_time_recorder.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/mojo/services/watch_time_recorder.h
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/media/mojo/services/watch_time_recorder_unittest.cc
[modify] https://crrev.com/ef3893f1f2c6c513f12f65d11e1ecc5b349a6ab3/tools/metrics/histograms/histograms.xml