Add an option to use the existing Xorg session with
chrome-remote-desktop.

The original idea of the patch: https://superuser.com/a/850359
--- a/chrome-remote-desktop	2022-04-23 17:34:24.118136150 +0300
+++ b/chrome-remote-desktop	2022-04-23 17:33:56.083833805 +0300
@@ -109,6 +109,8 @@
 
 X_LOCK_FILE_TEMPLATE = "/tmp/.X%d-lock"
 FIRST_X_DISPLAY_NUMBER = 20
+EXISTING_X_DISPLAY_FILE_PATH = os.path.join(CONFIG_DIR, "Xsession")
+X_SESSION_FILE_TEMPLATE = "/tmp/.X11-unix/X%d"
 
 # Amount of time to wait between relaunching processes.
 SHORT_BACKOFF_TIME = 5
@@ -514,6 +516,25 @@
       return True
     return False
 
+  def _use_existing_session(self):
+    with open(EXISTING_X_DISPLAY_FILE_PATH) as fh:
+      try:
+        display = int(fh.readline().rstrip())
+      except ValueError:
+        logging.error("Display is not a number")
+        sys.exit(1)
+    if not os.path.exists(X_SESSION_FILE_TEMPLATE % display):
+      logging.error("Xorg session file doesn't exist")
+      sys.exit(1)
+
+    logging.info("Using existing Xorg session: %d" % display)
+    self.child_env["DISPLAY"] = ":%d" % display
+    self.child_env["CHROME_REMOTE_DESKTOP_SESSION"] = "1"
+
+    # Set SSH_AUTH_SOCK to the file name to listen on.
+    if self.ssh_auth_sockname:
+      self.child_env["SSH_AUTH_SOCK"] = self.ssh_auth_sockname
+
   def launch_session(self, server_args, backoff_time):
     """Launches process required for session and records the backoff time
     for inhibitors so that process restarts are not attempted again until
@@ -522,10 +543,13 @@
     self._init_child_env()
     self.setup_audio()
     self._setup_gnubby()
-    self._launch_server(server_args)
-    if not self._launch_pre_session():
-      # If there was no pre-session script, launch the session immediately.
-      self.launch_desktop_session()
+    if os.path.exists(EXISTING_X_DISPLAY_FILE_PATH):
+      self._use_existing_session()
+    else:
+      self._launch_server(server_args)
+      if not self._launch_pre_session():
+        # If there was no pre-session script, launch the session immediately.
+        self.launch_desktop_session()
     self.server_inhibitor.record_started(MINIMUM_PROCESS_LIFETIME,
                                       backoff_time)
     self.session_inhibitor.record_started(MINIMUM_PROCESS_LIFETIME,