Reduce MediaLog spam and add a note about unsupported statuses.

content/browser/media/media_internals.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/media/media_internals.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/macros.h"
@@ skipping 406 matching lines @@
         ->Add(player_info.last_pipeline_status);
   } else if (player_info.has_audio) {
     UMA_HISTOGRAM_ENUMERATION("Media.PipelineStatus.AudioOnly",
                               player_info.last_pipeline_status,
                               media::PIPELINE_STATUS_MAX + 1);
   } else if (player_info.has_video) {
     UMA_HISTOGRAM_ENUMERATION("Media.PipelineStatus.VideoOnly",
                               player_info.last_pipeline_status,
                               media::PIPELINE_STATUS_MAX + 1);
   } else {
+    // Note: This metric can be recorded as a result of normal operation with
+    // Media Source Extensions. If a site creates a MediaSource object but never
+    // creates a source buffer or appends data, PIPELINE_OK will be recorded.
     UMA_HISTOGRAM_ENUMERATION("Media.PipelineStatus.Unsupported",
                               player_info.last_pipeline_status,
                               media::PIPELINE_STATUS_MAX + 1);
   }
   // Report whether video decoder fallback happened, but only if a video decoder
   // was reported.
   if (!player_info.video_decoder.empty()) {
     UMA_HISTOGRAM_BOOLEAN("Media.VideoDecoderFallback",
                           player_info.video_decoder_changed);
   }
@@ skipping 251 matching lines @@
           audio_streams_cached_data_.GetDictionary(cache_key, &existing_dict));
       existing_dict->MergeDictionary(value);
     }
   }
 
   if (CanUpdate())
     SendUpdate(SerializeUpdate(function, value));
 }
 
 }  // namespace content