Use existing Xorg session for chrome-remote-desktop

use_existing_session.patch

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	2021-04-05 11:53:16.537908500 +0000
+++ b/chrome-remote-desktop	2021-04-05 12:04:52.768536483 +0000
@@ -107,6 +107,8 @@
 
 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
@@ -774,14 +776,36 @@
         "Session output: ", SESSION_OUTPUT_TIME_LIMIT_SECONDS)
     output_filter_thread.start()
 
+  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, x_args):
     self._init_child_env()
     self._setup_pulseaudio()
     self._setup_gnubby()
-    self._launch_x_server(x_args)
-    if not self._launch_pre_session():
-      # If there was no pre-session script, launch the session immediately.
-      self.launch_x_session()
+    if os.path.exists(EXISTING_X_DISPLAY_FILE_PATH):
+      self._use_existing_session()
+    else:
+      self._launch_x_server(x_args)
+      if not self._launch_pre_session():
+        # If there was no pre-session script, launch the session immediately.
+        self.launch_x_session()
 
   def launch_host(self, host_config, extra_start_host_args):
     # Start remoting host