Rename 'unsafe-dynamic' to 'strict-dynamic'

In line with the spec change and discussion on WebAppSec:
https://github.com/w3c/webappsec-csp/commit/3476890664ada8efe2122301e6a4901cb12b520e

BUG=589380
R=jochen@chromium.org

Review-Url: https://codereview.chromium.org/2082613002
Cr-Commit-Position: refs/heads/master@{#400763}
6 files changed