Optional: Use nullopt and implicit construction in /modules/video_coding

Changes places where we explicitly construct an Optional to instead use
nullopt or the requisite value type only.

This CL was uploaded by git cl split.

Bug: None
Change-Id: Iedebf4dc56a973306e7d7e7649525879808dc72b
Reviewed-on: https://webrtc-review.googlesource.com/23578
Commit-Queue: Oskar Sundbom <ossu@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20878}
diff --git a/modules/video_coding/frame_object.cc b/modules/video_coding/frame_object.cc
index 72dd70e..6a31cfd 100644
--- a/modules/video_coding/frame_object.cc
+++ b/modules/video_coding/frame_object.cc
@@ -167,8 +167,8 @@
   rtc::CritScope lock(&packet_buffer_->crit_);
   VCMPacket* packet = packet_buffer_->GetPacket(first_seq_num_);
   if (!packet)
-    return rtc::Optional<RTPVideoTypeHeader>();
-  return rtc::Optional<RTPVideoTypeHeader>(packet->video_header.codecHeader);
+    return rtc::nullopt;
+  return packet->video_header.codecHeader;
 }
 
 }  // namespace video_coding