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/packet_buffer.cc b/modules/video_coding/packet_buffer.cc
index bf83083..9b3d93e 100644
--- a/modules/video_coding/packet_buffer.cc
+++ b/modules/video_coding/packet_buffer.cc
@@ -116,9 +116,9 @@
     UpdateMissingPackets(packet->seqNum);
 
     int64_t now_ms = clock_->TimeInMilliseconds();
-    last_received_packet_ms_ = rtc::Optional<int64_t>(now_ms);
+    last_received_packet_ms_ = now_ms;
     if (packet->frameType == kVideoFrameKey)
-      last_received_keyframe_packet_ms_ = rtc::Optional<int64_t>(now_ms);
+      last_received_keyframe_packet_ms_ = now_ms;
 
     found_frames = FindFrames(seq_num);
   }
@@ -458,7 +458,7 @@
 
 void PacketBuffer::UpdateMissingPackets(uint16_t seq_num) {
   if (!newest_inserted_seq_num_)
-    newest_inserted_seq_num_ = rtc::Optional<uint16_t>(seq_num);
+    newest_inserted_seq_num_ = seq_num;
 
   const int kMaxPaddingAge = 1000;
   if (AheadOf(seq_num, *newest_inserted_seq_num_)) {