/usr/include/unity/shell/ is in libunity-api-dev 7.108+16.04.20160322-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/unity/shell/application/
/usr/include/unity/shell/application/ApplicationInfoInterface.h
/usr/include/unity/shell/application/ApplicationManagerInterface.h
/usr/include/unity/shell/application/Mir.h
/usr/include/unity/shell/application/MirMousePointerInterface.h
/usr/include/unity/shell/application/MirPlatformCursor.h
/usr/include/unity/shell/application/MirSurfaceInterface.h
/usr/include/unity/shell/application/MirSurfaceItemInterface.h
/usr/include/unity/shell/launcher/
/usr/include/unity/shell/launcher/LauncherItemInterface.h
/usr/include/unity/shell/launcher/LauncherModelInterface.h
/usr/include/unity/shell/launcher/QuickListModelInterface.h
/usr/include/unity/shell/notifications/
/usr/include/unity/shell/notifications/Enums.h
/usr/include/unity/shell/notifications/ModelInterface.h
/usr/include/unity/shell/notifications/NotificationInterface.h
/usr/include/unity/shell/notifications/SourceInterface.h
/usr/include/unity/shell/scopes/
/usr/include/unity/shell/scopes/CategoriesInterface.h
/usr/include/unity/shell/scopes/FilterBaseInterface.h
/usr/include/unity/shell/scopes/FiltersInterface.h
/usr/include/unity/shell/scopes/NavigationInterface.h
/usr/include/unity/shell/scopes/OptionSelectorFilterInterface.h
/usr/include/unity/shell/scopes/OptionSelectorOptionsInterface.h
/usr/include/unity/shell/scopes/PreviewModelInterface.h
/usr/include/unity/shell/scopes/PreviewWidgetModelInterface.h
/usr/include/unity/shell/scopes/RangeInputFilterInterface.h
/usr/include/unity/shell/scopes/ResultsModelInterface.h
/usr/include/unity/shell/scopes/ScopeInterface.h
/usr/include/unity/shell/scopes/ScopesInterface.h
/usr/include/unity/shell/scopes/SettingsModelInterface.h
/usr/include/unity/shell/scopes/ValueSliderFilterInterface.h
/usr/include/unity/shell/scopes/ValueSliderValuesInterface.h