Improve 'Location.setProtocol' exception messages.

Rather than throwing a generic 'SyntaxError' exception, we should give
the developer some context about the reason behind the throw (the
protocol is invalid).

BUG=270033

Review URL: https://chromiumcodereview.appspot.com/22434004

git-svn-id: svn://svn.chromium.org/blink/trunk@156225 bbb929c8-8fbe-4397-9dbb-9b2b20218538