Add missing dep from chromium/ui/base to brave/app:brave_generated_resources_grit

[petemill]

This may be a strange technique to add a new BUILD.gn file at this specific path. Seeking advice on correct location for new .gn or .gni which is intended just to group chromium -> brave dependencies and minimize patch to 1 line.

Fix brave/brave-browser#3854

Investigation shows that we have modified a file in ui/base to include "chrome/grit/generated_resources.h" but that is rewritten to "brave/grit/brave_generated_resources.h" and there is no dep to the project which generates that.

Setting milestone of 0.63.x since this code was introduced with #1422

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 && npm run test-security) on
  • Windows
  • macOS
  • Linux
• 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

Test Plan:

Build

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

[petemill]

To be honest, this code probably shouldn't even be in ui/base since it's app-specific, but it's part of a shared component across webuis, and the only one that has dependencies on specific strings (rather than being passed from consumer). Plus, it avoids patching each chromium webui

   SetLoadTimeDataDefaults_ChromiumImpl(app_locale, localized_strings);
  localized_strings->SetString(
    "brToolbarSettingsTitle",
    l10n_util::GetStringUTF16(IDS_SETTINGS_SETTINGS)
  );
  localized_strings->SetString(
    "brToolbarBookmarksTitle",
    l10n_util::GetStringUTF16(IDS_BOOKMARK_MANAGER_TITLE)
  );
  localized_strings->SetString(
    "brToolbarDownloadsTitle",
    l10n_util::GetStringUTF16(IDS_DOWNLOAD_TITLE)
  );
  localized_strings->SetString(
    "brToolbarHistoryTitle",
    l10n_util::GetStringUTF16(IDS_HISTORY_TITLE)
  );
}

This could be fixed in a follow-up: brave/brave-browser#3856

[bsclifton]

Only failure is in the test-security step (marking the build as unstable). That is addressed with #2029

Per @mkarolin, this PR should fix official build failing on Windows