Why am I getting 'package cannot be authenticated' errors for google-chrome?
Solution 1:
There seems to be one file missing from the Google download server -- see http://crbug.com/249188.
Until that's fixed it would be OK, but not entirely safe, to update without checking the signature.
If someone can intercept and interfere with your internet traffic they could send you a malicious replacement for Chrome, so I wouldn't do this over public wifi, for example.
update: Now it's fixed.