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This CL:
1) Align the two ContentSecurityPolicy struct in between content and
   network::mojom
2) Add a content::ContentSecurityPolicy constructor from a
   network::mojom::ContentSecurityPolicy
3) Add several TODO for the frame-ancestor CSP checked out-of-blink.

This allows the future follow-ups:
  1) Replace content CSP by network::mojom CSP for every mojo IPC.
  2) Remove (gradually) every content CSP by the network::mojom ones.

Change-Id: I1b1e0658f77ce3141d263d7de09272d225a4f756
Bug: 1021462
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1926141
Auto-Submit: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719964}