1. Open a terminal. Clone this repository.

cd /tmp/repos # Or whatever you want
git clone https://github.com/ChiaMineJP/chip2-reference   

2. Open Chrome browser. Open extension page as the following image.

Now, when you open a new page, JavaScript on that page can access to window.chia API.
Note: This is just a demo so no actual communication to chia-blockchain happens.
If you're interested, you can develop actual intervention to chia-blockchain by updating content of https://github.com/ChiaMineJP/chip2-reference/blob/main/web_ext/src/background/api.js

See https://github.com/ChiaMineJP/chip2-reference/blob/e92991b7fc0f8a4acf4dc523cfcb5135876f9fd8/web_ext/docs/images/demo-1.mp4
Sorry, the file is 16MB and GitHub cannot play this mp4 directly. Just a 5 minutes instruction on how to install the demo extension and what can be tested with it.