Adds sha256/384/512 support to CSP script-hash and style-hash.

The Content Security Policy 1.1 spec calls for script-hash and style-hash to
support the regular suite of sha-2 hashes. This implements support for those
hashes under the CSP experimental flag.

BUG=327826

Review URL: https://codereview.chromium.org/171603019

git-svn-id: svn://svn.chromium.org/blink/trunk@167967 bbb929c8-8fbe-4397-9dbb-9b2b20218538