Support parsing of sgpd and sbgp boxes

media/formats/mp4/box_reader.h

Index: media/formats/mp4/box_reader.h
diff --git a/media/formats/mp4/box_reader.h b/media/formats/mp4/box_reader.h
index d4b608e78f9ea80c76f0dc6c95d20005d9b5c7ce..b1703cb7ac0b1550558f6f68426f4996b4aa7134 100644
--- a/media/formats/mp4/box_reader.h
+++ b/media/formats/mp4/box_reader.h
@@ -105,6 +105,9 @@ class MEDIA_EXPORT BoxReader : public BufferReader {
   // buffer position. Must be called before any of the *Child functions work.
   bool ScanChildren() WARN_UNUSED_RESULT;
 
+  // Return true if child with type |child.BoxType()| exists.
+  bool HasChild(Box* child) WARN_UNUSED_RESULT;
+
   // Read exactly one child box from the set of children. The type of the child
   // will be determined by the BoxType() method of |child|.
   bool ReadChild(Box* child) WARN_UNUSED_RESULT;