Copy duration to decrypted buffer after decryption.

This value is not copied during decryption, so it is missed.
We may consider copying it at CdmAdapter, but it seems CdmAdapter
ensures only fields in CdmInputBuffer. So this cl follows same
way as is_key_frame in DecryptingDemuxerStream.

Change-Id: I701aaa51d24792a3bdb41eaaf1cef12c751a58fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2348243Reviewed-by: Xiaohan Wang <xhwang@chromium.org>
Commit-Queue: JunHo Seo <junho0924.seo@lge.com>
Cr-Commit-Position: refs/heads/master@{#798035}

media/filters/decrypting_demuxer_stream.cc

@@ -305,10 +305,12 @@ void DecryptingDemuxerStream::OnBufferDecrypted(
 
   DCHECK_EQ(status, Decryptor::kSuccess);
 
-  // Copy the key frame flag from the encrypted to decrypted buffer, assuming
-  // that the decryptor initialized the flag to false.
-  if (pending_buffer_to_decrypt_->is_key_frame())
-    decrypted_buffer->set_is_key_frame(true);
+  // Copy the key frame flag and duration from the encrypted to decrypted
+  // buffer.
+  // TODO(crbug.com/1116263): Ensure all fields are copied by Decryptor.
+  decrypted_buffer->set_is_key_frame(
+      pending_buffer_to_decrypt_->is_key_frame());
+  decrypted_buffer->set_duration(pending_buffer_to_decrypt_->duration());
 
   pending_buffer_to_decrypt_ = nullptr;
   state_ = kIdle;