The content='...' parsing error is not a viewport error, so keep it separate

The parsing algorithm for the meta content attribute reports an error
for presense of ';'. It is currently using viewport error reporting, though
it is not tied to the viewport meta tag, but meta tags in general.

Review URL: https://chromiumcodereview.appspot.com/24025002

git-svn-id: svn://svn.chromium.org/blink/trunk@157367 bbb929c8-8fbe-4397-9dbb-9b2b20218538