Remove DCHECK since error is properly handled.

media/formats/mp4/box_reader.cc

Index: media/formats/mp4/box_reader.cc
diff --git a/media/formats/mp4/box_reader.cc b/media/formats/mp4/box_reader.cc
index 3b28bcaa3cfea0dfc681f4f65ae8ecebfbf06f83..2275258dc6376206230ff57d03475a103ec08808 100644
--- a/media/formats/mp4/box_reader.cc
+++ b/media/formats/mp4/box_reader.cc
@@ -200,7 +200,6 @@ bool BoxReader::ScanChildren() {
     pos_ += child.size();
   }
 
-  DCHECK(!err);
   return !err && pos_ == size_;
 }