Strictly speaking, Chrome is not ignoring a web standard, since the standard does not require this behavior (no "MUST" keyword).
Obviously a simple boolean is the wrong design here. But can you suggest a better one?
A better solution could be to just behave reasonably by default but allow the user to re-enable auto-fill with a single click.
Nevertheless, from their stance on the issue so far it stands to reason that the Chromium team would have objected to any efforts to tighten the spec, which would also have led us to this same situation.