Whitelist allowed URL patterns from system network context

[bbondy]

Fix brave/brave-browser#163

Let me know what you think about this work in progress. If we can find a way around the TODO comment on the bottom, then we can change to a DCHECK. I think logging is better than nothing for now though.

Submitter Checklist:

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).
• Tagged reviewers and labelled the pull request as needed.
• Request a security/privacy review as needed.
• Add appropriate QA labels (QA/Needed or QA/No-QA-Needed) to include the closed issue in milestone

Test Plan:

Reviewer Checklist:

• New files have MPL-2.0 license header.
• Request a security/privacy review as needed.
• Adequate test coverage exists to prevent regressions
• Verify test plan is specified in PR before merging to source

[bbondy]

If anyone wants to pick this up from here from me, feel free.
I'm purposely not canceling the URLs, but just causing debug assertions, I think that's the right first step towards this.

Please just use my branch ledger-urls and work on top of it.

[diracdeltas]

++ i like this approach

[bbondy]

Going ahead with merging this per a DM discussion with @diracdeltas and @jumde.

Work for being more aggressive about this check is added in an issue here:
brave/brave-browser#1090