Throw parse errors instead of just logging them to console

[jarek-foksa]

This way the parser could be used to validate properties and attributes, e.g.:

let isValidStyleAttributeValue = (value) => {
  try {
    CSSParser.parseAListOfDeclarations(value.trim());  
  }
  catch (error) {
    return false;
  }

  return true;
};

[tabatkins]

I wouldn't want to do that in general - one of CSS's nice features is that it'll parse any byte sequence you throw at it. But yeah, having some way to indicate that there was indeed a parse error would be nice for validation purposes.

[jarek-foksa]

But the parser is already throwing some parse errors, it would make more sense to either throw all parse errors or none at all.

[tabatkins]

You're right, I should definitely be consistent between the two.