getNumContainedPasses() used to compute the size of the vector on demand. It is
called repeated in loops (such as runOnFunction()) and it can be updated while
inside the loop.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@167759 91177308-0d34-0410-b5e6-96231b3b80d8