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 1ba0294bff3728799749fd862015053ee4b0e0ca..01c1f262be4df46751f48a01f36b7a04d1296eca 100644
--- a/media/formats/mp4/box_reader.h
+++ b/media/formats/mp4/box_reader.h
@@ -108,6 +108,9 @@ 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;