Improve README.chromium for WPTServe.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py
index 8e909db3cbb7d6f248ea6ddf5ddabd2905221df1..6040f80b90d0d07ad105cb142032e7149e56c4e2 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/wptserve.py
@@ -4,6 +4,8 @@
 
 """Start and stop the WPTserve servers as they're used by the layout tests."""
 
+import datetime
+import logging
 from webkitpy.layout_tests.servers import server_base
 
 
@@ -50,6 +52,13 @@ class WPTServe(server_base.ServerBase):
         self._keep_process_reference = True
         self._start_cmd = start_cmd
 
+        expiration_date = datetime.date(2025, 1, 4)
+        if datetime.date.today() > expiration_date - datetime.timedelta(30):
+            logging.getLogger(__name__).error(
+                'Pre-generated keys and certificates are going to be expired at %s.'
+                ' Please re-generate them by following steps in %s/README.chromium.'
+                % (expiration_date.strftime('%b %d %Y'), path_to_wpt_support))
+
     def _stop_running_server(self):
         # Clean up the pid file.
         if self._pid and not self._executive.check_running_pid(self._pid):