For one, there's likely few enough instances of MenuBarManager that the code
pessimization of using bitfields probably weighs worse than the space
optimization.  For another, the code generated by at least Clang trunk tends to
confuse Valgrind, <https://bugs.kde.org/show_bug.cgi?id=242137> "Valgrind on
LLVM compiled code reports tons of 'Conditional jump or move depends on
uninitialised' false positives".

Change-Id: I4c2ef22e7e54e2a220e2cb490ca0566af4f81f52