Read directly from 'senc' box when 'senc' box is present

media/test/data/README

Index: media/test/data/README
diff --git a/media/test/data/README b/media/test/data/README
index 499b97d8a004780ee25924305fbb4c091c0b38aa..4225f51b09677f766a6abd583e1301b38d542711 100644
--- a/media/test/data/README
+++ b/media/test/data/README
@@ -77,6 +77,7 @@ bear-640x360-a_frag-cenc.mp4 - A fragmented MP4 version of the audio track of be
 bear-640x360-a_frag-cenc-key_rotation.mp4 - A fragmented MP4 version of the audio track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2] with key rotation [3].
 bear-640x360-v_frag-cenc.mp4 - A fragmented MP4 version of the video track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2]  and with sample encryption auxiliary information in the beginning of mdat box.
 bear-640x360-v_frag-cenc-senc.mp4 - Same as above, but with sample encryption information stored in SampleEncryption ('senc') box.
+bear-640x360-v_frag-cenc-senc-no-saiz-saio.mp4 - Same as above, but without saiz and saio boxes.
 bear-640x360-v_frag-cenc-key_rotation.mp4 - A fragmented MP4 version of the video track of bear-640x360.mp4 encrypted (ISO CENC) using key ID [1] and key [2] with key rotation [3].
 bear-a_enc-a.webm - bear-320x240-audio-only.webm encrypted using key ID [1] and key [2].
 frame_size_change-av_enc-v.webm - third_party/WebKit/LayoutTests/media/resources/frame_size_change.webm encrypted using key ID [1] and key [2].