Fix pdf not loading by PDFJS after basic auth

[yrliou]

Fix brave/brave-browser#1788

Fix chromium upstream bug: https://bugs.chromium.org/p/chromium/issues/detail?id=805476
webRequest.onBeforeSendHeaders, webRequest.onSendHeaders, and webRequest.onHeadersReceived should be dispatched as the life cycle specified in https://developer.chrome.com/extensions/webRequest.

• 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:

See brave/brave-browser#1788 (comment)

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

[yrliou]

master: d6444a4
0.58.x: 4722ed5