Implement opus seek preroll for MediaSourceExtensions.

media/filters/source_buffer_range.h

Index: media/filters/source_buffer_range.h
diff --git a/media/filters/source_buffer_range.h b/media/filters/source_buffer_range.h
index 7e35dbdeee7275abb51c6a3d0ce2ab02dcc617ea..d407ec950dfffc0b9f8d5fbb39ccee3370306a95 100644
--- a/media/filters/source_buffer_range.h
+++ b/media/filters/source_buffer_range.h
@@ -37,6 +37,10 @@ class SourceBufferRange {
     ALLOW_GAPS
   };
 
+  int GetConfigIdAtTime(DecodeTimestamp timestamp);

[chcunningham, 2016/07/22 01:50:28]

TODO: document these functions

[wolenetz, 2016/12/02 00:18:49]

(Done)

+
+  bool SameConfigThruRange(DecodeTimestamp start, DecodeTimestamp end);
+
   // Sequential buffers with the same decode timestamp make sense under certain
   // conditions, typically when the first buffer is a keyframe. Due to some
   // atypical media append behaviors where a new keyframe might have the same