Start recording background video watch time.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index e0f7bc302ed1e6f2df7e654211077c1af2e0b057..349bdded66c8b3805c748db608e8c922cb8c445e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -118998,6 +118998,27 @@ from previous Chrome versions.
   <suffix name="AudioVideo.EmbeddedExperience"
       label="Watch time for downloaded media on Android with both an audio
              and video track."/>
+  <suffix name="AudioVideo.Background.All"
+      label="Background watch time for all media with both an audio and video
+             track."/>
+  <suffix name="AudioVideo.Background.AC"
+      label="Background watch time for all media with both an audio and video
+             track on AC power."/>
+  <suffix name="AudioVideo.Background.Battery"
+      label="Background watch time for all media with both an audio and video
+             track on battery power."/>
+  <suffix name="AudioVideo.Background.MSE"
+      label="Background watch time for MSE media with both an audio and video
+             track."/>
+  <suffix name="AudioVideo.Background.SRC"
+      label="Background watch time for SRC media with both an audio and video
+             track."/>
+  <suffix name="AudioVideo.Background.EME"
+      label="Background watch time for EME media with both an audio and video
+             track."/>
+  <suffix name="AudioVideo.Background.EmbeddedExperience"
+      label="Background watch time for downloaded media on Android with both
+             an audio and video track."/>
   <affected-histogram name="Media.WatchTime"/>
 </histogram_suffixes>