I wouldn't know about Google's C++ style guide, but Qt certainly have their own guidelines for Qt itself: https://wiki.qt.io/Qt_Coding_Style
There is a _clang-format file used by clang-format in the supermodule, which should be in line with the standard: https://github.com/qt/qt5/blob/dev/_clang-format
You're completely free to choose your own style for your projects using Qt, though.