Chrome extensions running in webpages share the DOM with the webpage. That's how they make modifications to the webpage.
They have their own javascript-wrappers around the DOM, so an extension is not vulnerable to a webpage overwriting DOM methods, but obviously the DOM still has the same content visible in it, and this can't protect extensions from using libraries which eval content within the DOM.
They have their own javascript-wrappers around the DOM, so an extension is not vulnerable to a webpage overwriting DOM methods, but obviously the DOM still has the same content visible in it, and this can't protect extensions from using libraries which eval content within the DOM.