$ qlist dev-qt/qtwebkit-5.6.0 /usr/include/qt5/QtWebKit/QtWebKitDepends /usr/include/qt5/QtWebKitWidgets/QtWebKitWidgetsDepends /usr/lib64/libQt5WebKitWidgets.so.5.6.0 /usr/lib64/qt5/mkspecs/modules/qt_lib_webkit.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkitwidgets.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkit_private.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkitwidgets_private.pri /usr/lib64/qt5/libexec/QtWebPluginProcess /usr/lib64/qt5/libexec/QtWebProcess /usr/lib64/qt5/qml/QtWebKit/qmldir /usr/lib64/qt5/qml/QtWebKit/experimental/qmldir /usr/lib64/qt5/qml/QtWebKit/experimental/libqmlwebkitexperimentalplugin.so /usr/lib64/qt5/qml/QtWebKit/libqmlwebkitplugin.so /usr/lib64/qt5/qml/QtWebKit/plugins.qmltypes /usr/lib64/libQt5WebKitWidgets.prl /usr/lib64/libQt5WebKit.so.5.6.0 /usr/lib64/libQt5WebKit.so.5 /usr/lib64/pkgconfig/Qt5WebKit.pc /usr/lib64/pkgconfig/Qt5WebKitWidgets.pc /usr/lib64/libQt5WebKit.so /usr/lib64/libQt5WebKitWidgets.so.5 /usr/lib64/libQt5WebKit.prl /usr/lib64/libQt5WebKitWidgets.so /usr/lib64/cmake/Qt5WebKit/Qt5WebKitConfigVersion.cmake /usr/lib64/cmake/Qt5WebKit/Qt5WebKitConfig.cmake /usr/lib64/cmake/Qt5WebKitWidgets/Qt5WebKitWidgetsConfig.cmake /usr/lib64/cmake/Qt5WebKitWidgets/Qt5WebKitWidgetsConfigVersion.cmake /usr/lib64/libQt5WebKit.so.5.6 /usr/lib64/libQt5WebKitWidgets.so.5.6
See the patch in bug #577574
With the call to make install_subtargets enough header files are installed to compile kdewebkit
Just a cross-reference: . . . https://bugs.gentoo.org/show_bug.cgi?id=577574#c14 ff.
Same with dev-qt/qtwebkit-5.7.0_alpha * Contents of dev-qt/qtwebkit-5.7.0_alpha: /usr /usr/include /usr/include/qt5 /usr/include/qt5/QtWebKit /usr/include/qt5/QtWebKit/QtWebKitDepends /usr/include/qt5/QtWebKitWidgets /usr/include/qt5/QtWebKitWidgets/QtWebKitWidgetsDepends /usr/lib64 /usr/lib64/cmake /usr/lib64/cmake/Qt5WebKit /usr/lib64/cmake/Qt5WebKit/Qt5WebKitConfig.cmake /usr/lib64/cmake/Qt5WebKit/Qt5WebKitConfigVersion.cmake /usr/lib64/cmake/Qt5WebKitWidgets /usr/lib64/cmake/Qt5WebKitWidgets/Qt5WebKitWidgetsConfig.cmake /usr/lib64/cmake/Qt5WebKitWidgets/Qt5WebKitWidgetsConfigVersion.cmake /usr/lib64/libQt5WebKit.prl /usr/lib64/libQt5WebKit.so -> libQt5WebKit.so.5.7.0 /usr/lib64/libQt5WebKit.so.5 -> libQt5WebKit.so.5.7.0 /usr/lib64/libQt5WebKit.so.5.7 -> libQt5WebKit.so.5.7.0 /usr/lib64/libQt5WebKit.so.5.7.0 /usr/lib64/libQt5WebKitWidgets.prl /usr/lib64/libQt5WebKitWidgets.so -> libQt5WebKitWidgets.so.5.7.0 /usr/lib64/libQt5WebKitWidgets.so.5 -> libQt5WebKitWidgets.so.5.7.0 /usr/lib64/libQt5WebKitWidgets.so.5.7 -> libQt5WebKitWidgets.so.5.7.0 /usr/lib64/libQt5WebKitWidgets.so.5.7.0 /usr/lib64/pkgconfig /usr/lib64/pkgconfig/Qt5WebKit.pc /usr/lib64/pkgconfig/Qt5WebKitWidgets.pc /usr/lib64/qt5 /usr/lib64/qt5/libexec /usr/lib64/qt5/libexec/QtWebPluginProcess /usr/lib64/qt5/libexec/QtWebProcess /usr/lib64/qt5/mkspecs /usr/lib64/qt5/mkspecs/modules /usr/lib64/qt5/mkspecs/modules/qt_lib_webkit.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkit_private.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkitwidgets.pri /usr/lib64/qt5/mkspecs/modules/qt_lib_webkitwidgets_private.pri blocks : quiterss, designer ...
QtQTBUG-52113: "Missing include headers in QtWebKit 5.6 source archives" . . . "The plan is to fix this for Qt 5.6.1." [ https://bugreports.qt.io/browse/QTBUG-52113 ]
With the changes made in bug #577574, headers are installed OK for me now.
*** This bug has been marked as a duplicate of bug 577574 ***