CSP: Adding a test for appended script elements.

How did we not have a test for this? Crazy.

BUG=429244

Review URL: https://codereview.chromium.org/701013004

git-svn-id: svn://svn.chromium.org/blink/trunk@184908 bbb929c8-8fbe-4397-9dbb-9b2b20218538