Prevent loading brave scheme url from javascript

[simonhong]

To fix this, brave scheme is registered to WebSecurityPolicy and
RequestScheme of ChildProcessSecurityPolicy::SecurityState.
Also, makes ProfileIOData::IsHandledProtocol consider brave scheme.

As brave scheme can be loaded only from brave scheme,
it should use chrome scheme instead of brave scheme in anchor tag..
Otherwise, that brave webui loading is prevented in brave webui from renderer.

Fix brave/brave-browser#2861
Fix brave/brave-browser#2849

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).
• Verified that these changes build without errors on
  • Windows
  • macOS
  • Linux
• Verified that these changes pass automated tests (npm test brave_unit_tests && npm test brave_browser_tests) on
  • Windows
  • macOS
  • Linux
• Ran git rebase master (if needed).
• 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/Yes or QA/No) to include the closed issue in milestone

Test Plan:

Test 1.

1. Navigate to https://world_languages.gitlab.io/bravepoc/
2. Click link
3. Check brave://settings is not loaded in new tab.

Test 2.

1. Navigate to brave://welcome
2. Move to Change your search engine page in welcome page
3. Click Settings button
4. Check settings page is opened in new tab

Test 3.

1. Open brave://settings
2. Right click on brave://sync
3. Check Save Link As... is disabled

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

[simonhong]

Will remove WIP after adding tests.

[bbondy]

Edited the PR description to not close brave/brave-browser#2777 but instead close brave/brave-browser#2861