307 Redirect when loading analytics.js in Chrome

307 Internal Redirect with Non-Authorative-Reason: Delegate indicates that the request was intercepted and modified (redirected) by a Chrome extension via the webRequest or declarative webRequest extension APIs.

You can find out which extension triggered the redirect as follows:

1. Visit chrome://net-internals/#events
2. Trigger the request (google analytics, in your case).
3. Go back to the chrome://net-internals/#events tab and look for a URL_REQUEST matching your request (you can use the searchbox to filter the search).
4. Click on the entry to show the log at the right side. You will see the extension name, extension ID and other information about the request:

t=7910 [st=0] +REQUEST_ALIVE  [dt=6]
t=7910 [st=0]   +URL_REQUEST_DELEGATE  [dt=5]
t=7910 [st=0]      DELEGATE_INFO  [dt=5]
                   --> delegate_info = "extension [Name of extension]"
t=7915 [st=5]      CHROME_EXTENSION_REDIRECTED_REQUEST
                   --> extension_id = "ebmlimjkpnhckbaejoagnjlgcdhdnjlb"
t=7915 [st=5]   -URL_REQUEST_DELEGATE
t=7915 [st=5]   +URL_REQUEST_START_JOB  [dt=1]
                 --> load_flags = 339804160 (BYPASS_DATA_REDUCTION_PROXY | MAYBE_USER_GESTURE | REPORT_RAW_HEADERS | VERIFY_EV_CERT)
                 --> method = "GET"
                 --> priority = "LOW"
                 --> url = "https://www.google-analytics.com/analytics.js"
t=7915 [st=5]      URL_REQUEST_REDIRECT_JOB
                   --> reason = "Delegate"
t=7915 [st=5]      URL_REQUEST_FAKE_RESPONSE_HEADERS_CREATED
                   --> HTTP/1.1 307 Internal Redirect
                       Location: about:blank
                       Non-Authoritative-Reason: Delegate

In this log sample, an extension with name "[Name of extension]" and extension ID "ebmlimjkpnhckbaejoagnjlgcdhdnjlb" redirected the request. After finding the extension name and/or ID, you can visit chrome://extensions and disable or remove the extension that modified the request.

In my case, the reason for the 307 redirect was more prosaic. Out of habit of using protocol-relative URLs, I've removed the protocol from the URL in the embedding script of the Google Universal Analytics, changing https://www.google-analytics.com/analytics.js to //www.google-analytics.com/analytics.js.

For example (don't try this at home):

(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','https://www.google-analytics.com/analytics.js','ga');

This is inadvisable since Google apparently serves the script and tracking requests only over https. So removing the protocol causes a redirect both when first embedding the script as well as in any(!) subsequent tracking request. In addition, as stated by Paul Irish in an update to his canonical post about protocol-relative URLs, this technique is no longer encouraged or indeed has merit:

Now that SSL is encouraged for everyone and doesn’t have performance concerns, this technique is now an anti-pattern. If the asset you need is available on SSL, then always use the https:// asset.

In my case, I have UBlock Origin activated on my browser. Once disconnected or site authorised, the internal redirections have stopped