CSP: Minor cleanup in ContentSecurityPolicy.php

CSP: Minor cleanup in ContentSecurityPolicy.php

Cleanups include;
- Remove elseif() path for cases where if has a return state
  and instead convert the elseif() into an if.
- Fix PHPDoc for non-existent parameter. Corrected parameter
  name.
- Add @throws phpdoc annotation for a method that could throw
  an exception.
- Remove unnecessary parentheses.
- Make sure line doesn't exceed 100 characters.

Change-Id: Ic2d882ae0c6f3859b5a268b1bfb50c8eafa294d9