Note: this list is generated by looking for the string for this theme hook, so it may include some references that are not actually using this theme hook.

layout_block_configure_ajax_update in modules/layout/layout.admin.inc
AJAX callback to update the underlying layout form after updating a block.
layout_block_remove_page in modules/layout/layout.admin.inc
Menu callback; Remove a block from a layout.
_layout_page_component_blocks_exist in modules/layout/layout.theme.inc
Utility function to return if a title component block is in a layout.
LayoutRendererEditor::getBlockLinks in modules/layout/plugins/renderers/layout_renderer_editor.inc
Render the links to display when editing a block.
LayoutRendererEditor::renderRegion in modules/layout/plugins/renderers/layout_renderer_editor.inc
Render a single layout region.
PageComponents::getContent in modules/system/block.page_components.inc
Return the content of a block.
system_block_info in modules/system/system.module
Implements hook_block_info().
system_preprocess_page_components in modules/system/system.theme.inc
Prepares variables for Page Component block templates.
system_theme in modules/system/system.module
Implements hook_theme().