Backport importer bugfixes

[iefremov]

Fixes brave/brave-browser#6521

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
  • Android
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that these changes pass automated tests (unit, browser, security tests) on
  • iOS
  • Linux
  • macOS
  • Windows
• Verified that all lint errors/warnings are resolved (npm run lint)
• 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
• Public documentation has been updated as necessary. For instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protection-Mode
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Custom-Headers
  • https://github.com/brave/brave-browser/wiki/Web-compatibility-issues-with-tracking-protection
  • https://github.com/brave/brave-browser/wiki/QA-Guide

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

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on.
• All relevant documentation has been updated.

[bsclifton]

Fix worked great for me! 😄

Will have to defer to @bridiver on the patching- this is a special case, since it's pulling in fixes that are in Canary but aren't in Stable yet... not sure how we want to handle that.

I've verified this is resolved in Chromium 80 (tested with Dev and Canary channels; and since 79 on Beta isn't finalized, they may uplift it). If we wanted to avoid patching master, we could PR specifically against 0.71 (C78), 0.72 (C79), and 0.73 (C79)

@bridiver WDYT?

[bsclifton]

++

[bbondy]

Can we uplift this pls? Also pls set the milestone on the issue to match the smallest version it landed on. Thank you! :)

[LaurenWags]

Verified with

Brave	1.3.17 Chromium: 78.0.3904.108 (Official Build) nightly (64-bit)
Revision	4b26898a39ee037623a72fcfb77279fce0e7d648-refs/branch-heads/3904@{#889}
OS	macOS Version 10.13.6 (Build 17G5019)

• Using the following Firefox version

• Confirmed FF displayed on brave://welcome as an option for Import.

• Confirmed FF displayed on brave://settings/importData as an option for Import.

• Confirmed was able to import History, Bookmarks, and Cookies from FF. Encountered Passwords, Search Engine, and Autofill are not imported from Firefox brave-browser#2198 for importing Passwords, Search Engine, and Autofill data.