It looks like all but one of these usages are inside -webkit prefixed pseudo selectors.

My understanding is that the appropriate replacement is to set the attribute contentEditable=false but I'm not familiar with how these CSS files are pulled in and used by the code or where the elements that use these rules are created.

tkent: I see you've worked with these CSS files a lot before. Do you have any recommendations for how to tackle this?

We need to remove these instances at the same time as we remove -webkit-user-modify support.

They were added for a security reason, we need to keep these elements non-editable. However, contentEditable=false won't prohibit from adding -webkit-user-modify:read-write*.

As for pseudo elements, we need to do nothing except remove -webkit-user-modify support because web authors can't add attributes to pseudo elements.

As for <meter>, we need a special code to disable contentEditable.

I don't think this issue should be in Blink>CSS.
We should move html.css and theme*.css to core/html/.

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