Address some violations of chromium-style.

webrtc/modules/rtp_rtcp/source/rtp_packet.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_packet.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_packet.cc b/webrtc/modules/rtp_rtcp/source/rtp_packet.cc
index 6b54be7b4c8abb424d74085ba7c35d78eb1a6087..c55b5c779f92ab2dbf5209678a6a20469321aa47 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_packet.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_packet.cc
@@ -62,6 +62,8 @@ Packet::Packet() : Packet(nullptr, kDefaultPacketSize) {}
 Packet::Packet(const ExtensionManager* extensions)
     : Packet(extensions, kDefaultPacketSize) {}
 
+Packet::Packet(const Packet&) = default;
+
 Packet::Packet(const ExtensionManager* extensions, size_t capacity)
     : buffer_(capacity) {
   RTC_DCHECK_GE(capacity, kFixedHeaderSize);