Fix memory leak in sample profile pass.

The problem here were the function analyses invoked by the function pass
manager from the new IPO pass. I looked at other IPO passes needing
dominance information and the only one that requires it (partial
inliner) does not use the standard dependency mechanism.

This patch mimics what the partial inliner does to compute dominance,
post-dominance and loop info. One thing I like about this approach is
that I can delay the computation of all this until I actually need it.

This should bring the ASAN buildbot back to green. If there's a better
way to fix this, I'll do it in a follow-up patch.

llvm-svn: 246066