Introduce the playback time into the MSE garbage collection.

media/filters/source_buffer_stream.h

Index: media/filters/source_buffer_stream.h
diff --git a/media/filters/source_buffer_stream.h b/media/filters/source_buffer_stream.h
index 95b2e0970b16ecbde8e60307e9bdc5d3e07625f8..c051b0b22ece640f65eefbb2136edec4e25609c0 100644
--- a/media/filters/source_buffer_stream.h
+++ b/media/filters/source_buffer_stream.h
@@ -86,6 +86,12 @@ class MEDIA_EXPORT SourceBufferStream {
   void Remove(base::TimeDelta start, base::TimeDelta end,
               base::TimeDelta duration);
 
+  // Update the playback time.
+  // This playback time is used to avoid garbage collecting buffers
+  // corresponding to the playback time:
+  // MSE spec - 2.4.4 SourceBuffer Monitoring.
+  void NotifyMediaTimeUpdate(base::TimeDelta media_time);
+
   // Changes the SourceBufferStream's state so that it will start returning
   // buffers starting from the closest keyframe before |timestamp|.
   void Seek(base::TimeDelta timestamp);
@@ -368,6 +374,11 @@ class MEDIA_EXPORT SourceBufferStream {
   // emptied.
   SourceBufferRange* selected_range_;
 
+  // Current media time.
+  // This does not need to be very accurate as long as it represents a lower
+  // bound of the media time.
+  base::TimeDelta current_media_time_;
+
   // Queue of the next buffers to be returned from calls to GetNextBuffer(). If
   // |track_buffer_| is empty, return buffers from |selected_range_|.
   BufferQueue track_buffer_;