Add embedder-specific headers to HTTP CONNECT tunnel request

net/http/http_proxy_client_socket.cc

Index: net/http/http_proxy_client_socket.cc
diff --git a/net/http/http_proxy_client_socket.cc b/net/http/http_proxy_client_socket.cc
index 3d9eadd48353eaa61095581bcc22034e3e510e7f..06a4ac9c5e653e5125e60b1e0bd7e0045561f572 100644
--- a/net/http/http_proxy_client_socket.cc
+++ b/net/http/http_proxy_client_socket.cc
@@ -6,6 +6,7 @@
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
+#include "base/callback.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "net/base/auth.h"
@@ -35,6 +36,8 @@ HttpProxyClientSocket::HttpProxyClientSocket(
     bool tunnel,
     bool using_spdy,
     NextProto protocol_negotiated,
+    const base::Callback<void(const HostPortPair&, HttpRequestHeaders*)>&
+        before_proxy_tunnel_request_callback,
     bool is_https_proxy)
     : io_callback_(base::Bind(&HttpProxyClientSocket::OnIOComplete,
                               base::Unretained(this))),
@@ -53,6 +56,9 @@ HttpProxyClientSocket::HttpProxyClientSocket(
       protocol_negotiated_(protocol_negotiated),
       is_https_proxy_(is_https_proxy),
       redirect_has_load_timing_info_(false),
+      proxy_server_(proxy_server),
+      before_proxy_tunnel_request_callback_(
+          before_proxy_tunnel_request_callback),
       net_log_(transport_socket->socket()->NetLog()) {
   // Synthesize the bits of a request that we actually use.
   request_.url = request_url;
@@ -403,6 +409,10 @@ int HttpProxyClientSocket::DoSendRequest() {
   if (request_line_.empty()) {
     DCHECK(request_headers_.IsEmpty());
     HttpRequestHeaders authorization_headers;
+    if (!before_proxy_tunnel_request_callback_.is_null()) {
+      before_proxy_tunnel_request_callback_.Run(proxy_server_,
+                                           &authorization_headers);
+    }
     if (auth_->HaveAuth())
       auth_->AddAuthorizationHeader(&authorization_headers);
     BuildTunnelRequest(request_, authorization_headers, endpoint_,