Media: Add MEDIALOG_CREATED event

media/base/media_log_event.h

Index: media/base/media_log_event.h
diff --git a/media/base/media_log_event.h b/media/base/media_log_event.h
index 73d81dcaf1da192770a812c8c12ce40d32e4663a..e02459f7ad8cabaebc1015ad15aa4751628634d3 100644
--- a/media/base/media_log_event.h
+++ b/media/base/media_log_event.h
@@ -30,6 +30,17 @@ struct MediaLogEvent {
   }
 
   enum Type {
+    // A MediaLog is being created.
+    // params: none.
+    //
+    // This event allows the browser service to discard state but still
+    // determine which events belong to new players. It must be logged exactly
+    // once, as the first event in a MediaLog.
+    //
+    // Note: RenderMediaLog sends this event automatically; future
+    // implementations of MediaLog should do so as well.
+    MEDIALOG_CREATED,
+
     // A WebMediaPlayer is being created or destroyed.
     // params: none.
     WEBMEDIAPLAYER_CREATED,