What steps will reproduce the problem?
(1) Turn on Accessibility Inspection experiment on ChromeOS
(2) Restart devtools, then click "Accessibility" tab in Elements pane

What is the expected result?

Accessibility inspection tools appear.

What happens instead?

Blank tab appears.

Console output:

https://chrome-devtools-frontend.appspot.com/serve_file/@0/accessibility/accessibility_module.js Failed to load resource: the server responded with a status of 404 ()
inspector.html:1 XMLHttpRequest cannot load https://chrome-devtools-frontend.appspot.com/serve_file/@0/accessibility/accessibility_module.js. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'chrome-devtools://devtools' is therefore not allowed access. The response had HTTP status code 404.
inspector.js:22 Empty response arrived for script 'https://chrome-devtools-frontend.appspot.com/serve_file/@0/accessibility/accessibility_module.js'
evaluateScript @ inspector.js:22
inspector.js:109 Uncaught (in promise) Error: Could not instantiate: Accessibility.AccessibilitySidebarView
    at Runtime.Extension._createInstance (inspector.js:109)