request #11008: Pull request karma tests sometimes fails for no reason

This seems like an usual issue [1][2] which is probably related
to the server load.

While not fixing the root cause, this contribution uses a commonly
employed technique: it doubles how long Karma wait for a message
from the browser before disconnecting from it.

[1] karma-runner/karma#598
[2] codymikol/karma-webpack#8

Change-Id: Id809a3c6d518edda6835b9b97eb3e53e438a8cb8

plugins/pullrequest/www/js/angular/karma.config.js

@@ -45,5 +45,6 @@ module.exports = {
      * the aesthetic advantage of not launching a browser every time you save.
      */
     browsers: [process.platform !== 'linux' ? 'ChromeHeadless' : 'ChromiumHeadless'],
+    browserNoActivityTimeout: 20000,
     logLevel: 'INFO'
 };