Part 3.1: Is policy list subsumed under subsuming policy?

This is part of an experimental feature Embedding-CSP.

This patch introduces CSPDirectiveList subsumption.
We aggregate SourceListDirectives based on their directive
names (or default directives otherwise) to check if it subsumes
under the embedding csp.

Note: There is only one SourceListDirective for each directive
name type specified by Embedding CSP since it specifies only one
policy.
+ We only consider scheme source /host source expressions to this
point.

Separate patches will be devoted to consideration of
'unsafe-inline' etc.

BUG=647588

Review-Url: https://codereview.chromium.org/2474903002
Cr-Commit-Position: refs/heads/master@{#434667}
5 files changed