Part 3.2: Is policy list subsumed under subsuming policy?
This is part of an experimental feature Embedding-CSP.
Here we add support for `self` source, which gets compiled
to CSPSources for normalization (finding intersection) and
subsumption.
For example, if the secure origin is "https://example.test/"
then for a list of policies:
`
Content-Security-Policy: script-src 'self'
Content-Security-Policy: script-src https://example.test/
`
an intersection would be:
`Content-Security-Policy: script-src https://example.test/`
BUG=647588
Review-Url: https://codereview.chromium.org/2519103005
Cr-Commit-Position: refs/heads/master@{#435883}
4 files changed
