Bump chromium to a264339194bfa02f5ecb3b8cba449 (master)

Editor assessment

This chromium roll follows the established roll-commit convention: the subject names the dependency, the pinned hash, and the branch (master), which is the atomic unit of information for a roll where per-commit detail lives upstream. The chore type is correct and the co-authored-by trailers attribute the rollers properly. No body is expected for this commit kind, since the hash itself is the reference; nothing is missing that the convention owes. No footers beyond attribution, and hygiene is clean. For its genre the message is complete, accurate, and easy to act on.