8 files declare their use of Breadcrumb in Zircon Profile 8

BookBreadcrumbBuilder.php in core/modules/book/src/BookBreadcrumbBuilder.php

Contains \Drupal\book\BookBreadcrumbBuilder.

BreadcrumbManagerTest.php in core/tests/Drupal/Tests/Core/Breadcrumb/BreadcrumbManagerTest.php

Contains \Drupal\Tests\Core\Breadcrumb\BreadcrumbManagerTest.

BreadcrumbTest.php in core/tests/Drupal/Tests/Core/Breadcrumb/BreadcrumbTest.php

Contains \Drupal\Tests\Core\Breadcrumb\BreadcrumbTest.

CommentBreadcrumbBuilder.php in core/modules/comment/src/CommentBreadcrumbBuilder.php

Contains \Drupal\comment\CommentBreadcrumbBuilder.

ForumBreadcrumbBuilderBase.php in core/modules/forum/src/Breadcrumb/ForumBreadcrumbBuilderBase.php

Contains \Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase.

menu_ui.module in core/modules/menu_ui/menu_ui.module

Allows administrators to customize the site's navigation menus.

PathBasedBreadcrumbBuilder.php in core/modules/system/src/PathBasedBreadcrumbBuilder.php

Contains \Drupal\system\PathBasedBreadcrumbBuilder.

TermBreadcrumbBuilder.php in core/modules/taxonomy/src/TermBreadcrumbBuilder.php

Contains \Drupal\taxonomy\TermBreadcrumbBuilder.