Reduce report timeout in CSP reporting API WPT tests (#21131)

In order to test that no report was sent, the WPT tests set a timeout
and check that no report was received once it expires. The current value
of the timeout is a bit too long, causing the test to sometimes timeout
in a flaky manner. This CL reduces the timeout and re-enables the test.

Bug: 850170
Change-Id: Ibc39291fa0bcfafa94cd84233b78973d74afff1c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1995261
Auto-Submit: Camille Lamy <clamy@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Camille Lamy <clamy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731947}

content-security-policy/support/checkReport.sub.js

@@ -47,7 +47,7 @@
   // is to wait for some reasonable amount of time and if no report has been
   // received to conclude that no report has been generated. These timeouts must
   // not exceed the test timeouts set by vendors otherwise the test would fail.
-  var timeout = document.querySelector("meta[name=timeout][content=long]") ? 25 : 5;
+  var timeout = document.querySelector("meta[name=timeout][content=long]") ? 20 : 3;
   var reportLocation = location.protocol + "//" + location.host + "/content-security-policy/support/report.py?op=retrieve_report&timeout=" + timeout + "&reportID=" + reportID;
 
   if (testName == "") testName = "Violation report status OK.";