Improve README.chromium for WPTServe.

Also, wptserve.py shows a warning before certificate expiration.

BUG=623613
NOTRY=true

Review-Url: https://codereview.chromium.org/2443863002
Cr-Commit-Position: refs/heads/master@{#427270}

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):

third_party/WebKit/Tools/Scripts/webkitpy/thirdparty/wpt/README.chromium

@@ -51,8 +51,8 @@ checked in and try to keep the list as small as possible (use what you need).
 certs/
 ======
 This directory contains a private key and a certificate of WPTServe, and files
-for self-signed CA. WPTServe generates them on the fly with "openssl" command in
-the default setting, but we check in pre-generated files to avoid "openssl"
+for self-signed CA. By default, WPTServe generates these files using the
+"openssl" command, but we check in pre-generated files to avoid "openssl"
 dependency.
 
 These certificates will expire in January 2025. Here is an instruction to
@@ -99,11 +99,13 @@ index 5b571c0..223a18b 100644
 6. Replace certs/ with wpt/_certs/
    % rm -fr certs
    % mv wpt/_certs certs
-7. Look at *.pem, and update "January 2025" in this document to new expiration
-   date.
+7. Look at *.pem, and update "January 2025" in this document and expiration_date
+   in wptserve.py to new expiration date.
 8. git commit -a
 9. git cl upload, etc.
 
+TODO(tkent): Make a script to re-generate keys and certificates.
+
 **
 
 Rolling in WPT
@@ -136,9 +138,6 @@ https://github.com/w3c/web-platform-tests/blob/master/README.md
 Also, check out the WPTServe Documentation
 (https://wptserve.readthedocs.org/en/latest/).
 
-For setting up SSL, refer to Tools/Scripts/webkitpy/thirdparty/wpt/wpt/_certs
-(which gets generated on the first run).
-
 Note that editing /etc/hosts is not required for run-webkit-tests since
 content_shell is invoked with flags to map all *.test domains to 127.0.0.1.