[Media] Add a feature flag to pause bg video only players.

media/base/media_switches.cc

Index: media/base/media_switches.cc
diff --git a/media/base/media_switches.cc b/media/base/media_switches.cc
index 28e749dc8dbc8cbb2ae6cb3776e349355adfc14b..03b4c7685e31a19cc1f8df94f6e719030fa783ec 100644
--- a/media/base/media_switches.cc
+++ b/media/base/media_switches.cc
@@ -173,6 +173,10 @@ const base::Feature kResumeBackgroundVideo {
 const base::Feature kBackgroundVideoTrackOptimization{
     "BackgroundVideoTrackOptimization", base::FEATURE_DISABLED_BY_DEFAULT};
 
+// Let video without audio be paused when it is playing in the background.
+const base::Feature kBackgroundVideoPauseOptimization{
+    "BackgroundVideoPauseOptimization", base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Make MSE garbage collection algorithm more aggressive when we are under
 // moderate or critical memory pressure. This will relieve memory pressure by
 // releasing stale data from MSE buffers.