The console error is:

Mixed Content: The page at 'https://pdfium-review.googlesource.com/c/2153/' was loaded over HTTPS, but requested an insecure resource 'http://pdfium-review.googlesource.com/changes/I60fc6176523ece112d41fdefc767aaefedfae2db'. This request has been blocked; the content must be served over HTTPS.
CQPlugin.watch @ commitqueue.js:44