If you desire to use your favorite keyboard layout but it is not available by default in Chrome OS or in this repository then a new extension will need to be created. In this directory you can find some examples to use as a template for creating your own. Please feel free to submit a pull request to share your extension with the world.
The first thing to do is determine if you can take the simple route or if your extension will require more effort. If your layout is already in the version of xkeyboard-config that is available in Chrome OS you are nearly ready.
On your Chrome OS device, open a new browser tab and go to chrome://version.
Find both the "Google Chrome" and the "Platform" version numbers. My device, as
I write this, is "Google Chrome" 85.0.4183.84 and "Platform" 13310.59.0.
Navigate to the Chromium source repository. Click on the branch named 'release-R-.B', e.g. release-R85-13310.B. Click the 'x11-misc' and then 'xkeyboard-config' links. You will now need to compare the version number listed for the xkeyboard-config ebuild file. The revision I am using for this example is 2.27.
Going back to the xkeyboard-config repository and update the source viewer to the tag based on that release version. In GitHub you click the branch selection menu, click "Tags", and then select the appropriate version.
Now browse down to the 'symbols' directory and look for the country code appropriate for your layout. Search the file you select for the layout name. For example, search 'dvorak'.
If the layout exists in the version of xkeyboard-config that is running on your build of Chrome OS you can easily create a new extension with just an extension manifest file. Head over to the XKB section for details on how to proceed.
If, however, the layout does not exist then you have a few options to consider. If the layout exists in a version of xkeyboard-config that is newer than that running on Chrome OS then you could create a bug requesting a new version of xkeyboard-config be built and included. This may take a while.
The other option is to create your own extension using some sort of key combination mapping in JavaScript. Head over to the remap section for details on how to proceed.