Doesn't seem to work, even though it does for other symbols (very well done - nice work!).
Steps to replicate:
Add a new C++ Source File to a C++ project. Type a line like
std::vector<int> a;
The refactor context-menu doesn't ever have the 'Add Include' member, whether I invoke it over std, vector, int, a or any of the symbols.
Adding text like this:
int fn()
{
printf("test");
}
and invoking the refactor menu over 'printf' does show 'Add Include'.
It doesn't make any difference if I put the declaration of a in fn - I still don't get the Add Include option.