CSP: Separate side-effects of parsing from the parsing code.

This patch shouldn't have any practical effect on CSP, but it will make
it straightforward to separate side-effects from parsing in a future
patch.

BUG=411889

Review URL: https://codereview.chromium.org/550223002

git-svn-id: svn://svn.chromium.org/blink/trunk@181632 bbb929c8-8fbe-4397-9dbb-9b2b20218538