Report video_rotation in DecryptingDemuxerStream

DecryptingDemuxerStream should report proper video_rotation
of the underlying DemuxerStream.

BUG=none

Review URL: https://codereview.chromium.org/1175563005

Cr-Commit-Position: refs/heads/master@{#333650}

media/filters/decrypting_demuxer_stream.cc

@@ -139,7 +139,7 @@ bool DecryptingDemuxerStream::SupportsConfigChanges() {
 }
 
 VideoRotation DecryptingDemuxerStream::video_rotation() {
-  return VIDEO_ROTATION_0;
+  return demuxer_stream_->video_rotation();
 }
 
 DecryptingDemuxerStream::~DecryptingDemuxerStream() {