This CL adds methods to manipulate RTP header extension, particularly

content/browser/renderer_host/p2p/socket_host_tcp.cc

Index: content/browser/renderer_host/p2p/socket_host_tcp.cc
diff --git a/content/browser/renderer_host/p2p/socket_host_tcp.cc b/content/browser/renderer_host/p2p/socket_host_tcp.cc
index 007472c07ee6ee44b0daed0049e7c0da4f365944..cf995bc307149198f212a7af1dc8fc2cc88de66f 100644
--- a/content/browser/renderer_host/p2p/socket_host_tcp.cc
+++ b/content/browser/renderer_host/p2p/socket_host_tcp.cc
@@ -18,6 +18,7 @@
 #include "net/socket/tcp_client_socket.h"
 #include "net/url_request/url_request_context.h"
 #include "net/url_request/url_request_context_getter.h"
+#include "third_party/libjingle/source/talk/base/asyncpacketsocket.h"
 
 namespace {
 
@@ -454,6 +455,9 @@ void P2PSocketHostTcp::DoSend(const net::IPEndPoint& to,
   *reinterpret_cast<uint16*>(buffer->data()) = base::HostToNet16(data.size());
   memcpy(buffer->data() + kPacketHeaderSize, &data[0], data.size());
 
+  talk_base::PacketOptions options;
+  MaybeUpdateRtpSendTimeExtn(buffer->data(), buffer->BytesRemaining(), options);
+
   WriteOrQueue(buffer);
 }
 
@@ -519,6 +523,10 @@ void P2PSocketHostStunTcp::DoSend(const net::IPEndPoint& to,
       new net::DrainableIOBuffer(new net::IOBuffer(size), size);
   memcpy(buffer->data(), &data[0], data.size());
 
+  // Update HMAC before writing padding bytes at the end.
+  talk_base::PacketOptions options;
+  MaybeUpdateRtpSendTimeExtn(buffer->data(), data.size(), options);
+
   if (pad_bytes) {
     char padding[4] = {0};
     DCHECK_LE(pad_bytes, 4);