Add experimental option for TCP FastOpen....

net/http/http_proxy_client_socket.cc

Index: net/http/http_proxy_client_socket.cc
===================================================================
--- net/http/http_proxy_client_socket.cc	(revision 63182)
+++ net/http/http_proxy_client_socket.cc	(working copy)
@@ -185,6 +185,14 @@
   return false;
 }
 
+bool HttpProxyClientSocket::UsingTCPFastOpen() const {
+  if (transport_.get() && transport_->socket()) {
+    return transport_->socket()->UsingTCPFastOpen();
+  }
+  NOTREACHED();
+  return false;
+}
+
 int HttpProxyClientSocket::Read(IOBuffer* buf, int buf_len,
                                 CompletionCallback* callback) {
   DCHECK(!user_callback_);