CSP 1.1: <meta> delivery should be ignored outside <head>.

Spec: http://w3c.github.io/webappsec/specs/content-security-policy/csp-specification.dev.html#html-meta-element

BUG=335489

Review URL: https://codereview.chromium.org/132563006

git-svn-id: svn://svn.chromium.org/blink/trunk@167171 bbb929c8-8fbe-4397-9dbb-9b2b20218538