face: detect websocket connection failure using ping/pong messages.

Change-Id: I66ef6a3921a56f1bb8e49fb6fdb4fa14b6a379c7
Refs: #1903
diff --git a/daemon/face/websocket-face.hpp b/daemon/face/websocket-face.hpp
index 3f2a932..81a1111 100644
--- a/daemon/face/websocket-face.hpp
+++ b/daemon/face/websocket-face.hpp
@@ -28,6 +28,7 @@
 
 #include "face.hpp"
 #include "core/logger.hpp"
+#include "core/scheduler.hpp"
 
 #ifndef HAVE_WEBSOCKET
 #error "Cannot include this file when WebSocket support is not enabled"
@@ -64,11 +65,18 @@
   close();
 
   void
+  setPingEventId(EventId& id)
+  {
+    m_pingEventId = id;
+  }
+
+  void
   handleReceive(const std::string& msg);
 
 private:
   websocketpp::connection_hdl m_handle;
   websocket::Server& m_server;
+  EventId m_pingEventId;
   bool m_closed;
 };