Add about_flag for experimenting MediaSession on Desktop

media/base/media_switches.h

Index: media/base/media_switches.h
diff --git a/media/base/media_switches.h b/media/base/media_switches.h
index b1ed8408301b2c182525387b7e42f72b56e8b2e2..c50f4c344604ecaca12f075c19e7fcb2487cd7a6 100644
--- a/media/base/media_switches.h
+++ b/media/base/media_switches.h
@@ -45,7 +45,11 @@ MEDIA_EXPORT extern const char kUseCras[];
 
 #if !defined(OS_ANDROID)
 MEDIA_EXPORT extern const char kEnableDefaultMediaSession[];
-#endif
+#endif  // !defined(OS_ANDROID)
+
+#if !defined(OS_ANDROID) && defined(ENABLE_PLUGINS)
+MEDIA_EXPORT extern const char kEnableDefaultMediaSessionWithFlash[];
+#endif  // defined(ENABLE_PLUGINS)
 
 MEDIA_EXPORT extern const char kUseFakeDeviceForMediaStream[];
 MEDIA_EXPORT extern const char kUseFileForFakeVideoCapture[];
@@ -77,10 +81,6 @@ namespace media {
 MEDIA_EXPORT extern const base::Feature kMediaFoundationH264Encoding;
 #endif  // defined(OS_WIN)
 
-#if defined(ENABLE_PLUGINS)
-MEDIA_EXPORT extern const base::Feature kFlashJoinsMediaSession;
-#endif  // defined(ENABLE_PLUGINS)
-
 MEDIA_EXPORT extern const base::Feature kNewAudioRenderingMixingStrategy;
 MEDIA_EXPORT extern const base::Feature kOverlayFullscreenVideo;
 MEDIA_EXPORT extern const base::Feature kResumeBackgroundVideo;