Let user take screenshots when reporting Android webcompat issues

[vadimstruts]

Resolves brave/brave-browser#36486

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

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, 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-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

Case 1

1. Go to any web page
2. Open Brave Shields pop up dialog.
3. Switch off Brave Shields if It is ON.
4. Click "Report broken site".
5. Click "Submit"
6. Make sure screenshot has not been sent with the report.

Case 2

1. Go to any web page
2. Open Brave Shields pop up dialog.
3. Switch off Brave Shields if It is ON.
4. Click "Report broken site".
5. Click the checkbox "Include screenshot of the current page"
6. Click "View screenshot" to check the screenshot of the current page is ready
7. Click "Submit"
8. Make sure the screenshot has been sent in context of the webcompat report

[mkarolin]

strings++

[AlexeyBarabash]

shouldn't be here something like

if (isCancelled()) {
   mCallback.OnScrrenshotReady(pngBytes);
   return;
}

?

[AlexeyBarabash]

👍
lgtm with few minor notices

[deeppandya]

Asynctask is deprecated with api 30 : https://developer.android.com/reference/android/os/AsyncTask.html. we should use executors here.

[deeppandya]

Good explanation on why we shouldn't use asynctask. : https://proandroiddev.com/a-quick-story-about-async-callbacks-memory-leaks-weakreferences-and-misconceptions-78003b3d6b26

[vadimstruts]

done

[deeppandya]

LGTM

[deeppandya]

Thank you @vadimstruts for the changes here.