CSP: Add a mechanism to disable CSP 1.1 for layout tests.

In order to test some changes to report-only for CSP 1.1, we need a
mechanism by which we can disable 1.1 when running layout tests. This
patch adds a flag to 'window.internal.settings', and toggles it off for
report-only tests. This changes the result by removing the
'effective-directive' attribute from the report JSON, which was first
added in 1.1.

BUG=335489

Review URL: https://codereview.chromium.org/131103003

git-svn-id: svn://svn.chromium.org/blink/trunk@165446 bbb929c8-8fbe-4397-9dbb-9b2b20218538