As of commit cb20372465f875ff4fbf2a04f0951430207f7b7a, according to tokei, in all of fuchsia there are 792k lines of C, 880k lines of C header, 1.711M lines of C++, 10k lines of C++ header, and 2.585M lines of Rust. In the zircon subdir, there are 569k lines of C, 300k lines of C header and 473k lines of C++.
I know what it means to use C++ as a nicer C, but what does it mean to use C as a restricted C++?
C as a restricted C++ could be probably something like GLib: a deeply object-oriented library (nowadays C++ isn't about OOP at all though).