Additional food for thought. Elsewhere, in 4.10.5.1.2 (Text (type=text))...
"If the element is mutable, its value SHOULD (emphasis mine) be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the element's value."
"If the element is mutable, its value SHOULD (emphasis mine) be editable by the user. User agents must not allow users to insert U+000A LINE FEED (LF) or U+000D CARRIAGE RETURN (CR) characters into the element's value."
https://html.spec.whatwg.org/multipage/input.html
So, according to this spec, the UA is allowed to make an input field type=text non-editable if it so chooses.
Would you argue that this is another place where Chrome would be allowed to act in a manner differently than expected, because "SHOULD" was used?