Pass the desktop session ID to the remoting network process.

remoting/host/desktop_session_win.h

Index: remoting/host/desktop_session_win.h
diff --git a/remoting/host/desktop_session_win.h b/remoting/host/desktop_session_win.h
index 1c58fa35e20c37c5e90d7fb53a791c0212402d14..9b681c4835039fd7499305df4f3844e371a94a47 100644
--- a/remoting/host/desktop_session_win.h
+++ b/remoting/host/desktop_session_win.h
@@ -131,6 +131,10 @@ class DesktopSessionWin
 
   base::Time last_timestamp_;
 
+  // The id of the current desktop session being remoted or UINT32_MAX if no
+  // session exists.
+  int session_id_ = UINT32_MAX;
+
   DISALLOW_COPY_AND_ASSIGN(DesktopSessionWin);
 };