Avoid crashing importer utility process if Muon bookmarks data is malformed

[garrettr]

Resolves brave/brave-browser#2517.

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:

1. Download this example of a corrupted session-store-1.
2. Start Muon with a fresh profile (backup your old profile, if necessary)
3. Close Muon
4. Copy the corrupted session-store-1 into Muon's user data directory
5. Open Muon again; create a new window with some random tabs in it. This is one way to make sure the importer process got through to the last step, which is importing open windows and tabs.
6. Close Muon
7. Open Brave Core.
8. Import bookmarks and settings.... Choose "Brave (old)" in the drop-down menu and make sure all of the importer data type checkboxes are checked.
9. Click Import.

Import should succeed and all data types should be imported (did the window you had open in Muon get opened in Brave Core?).

You should still have all of your bookmarks except for the ones that were intentionally corrupted. The importer should skip importing those without causing the importer utility process to crash.

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

[kjozwiak]

@garrettr uplift request to 0.58.x approved after deliberating with @rebron 👍 Please add/remove all needed labels and ensure that the associated issues are moved into the correct milestone.

Before requesting uplift approval for beta, please make sure that the PR has already been merged into master/nightly and dev.

[garrettr]

• master: 233876e
• 0.60.x: 8762ff1
• 0.59.x: b642277
• 0.58.x: 6842ae1