Chrome MV3 use_dynamic_url test page

This is a test page for the use_dynamic_url web_accessible_resources option. use_dynamic_url is supposed to randomise the URL for web_accessible_resources, to prevent websites from knowing the URL in advance. This helps prevent websites detecting that an extension (e.g. ad blocker) is installed by requesting a bunch of known web_accessible_resources.

Install the test extension in Chrome, and then refresh the page. The static URL request should be successful, but the dynamic URL request should fail. See also the extension source and https://crbug.com/1383176.