Missing <QtGui/QWindow> include in gui/kernel/qplatformwindow_p.h

gui/kernel/qplatformwindow_p.h contains references to QWindow but does not include <QtGui/QWindow>.

These QWindow references end up in moc_qplatformwindow_p.cpp which cannot be compiled on its own due to no QWindow declaration being in scope. This is masked because one of the other files included earlier in QtGui's mocs_compilation.cpp (presumably moc_qplatformservices.cpp) includes <QtGui/QWindow>.