[SampleFDO] Treat names in profile as not cold only when profile symbol list

is available

In rL372232, we treated names showing up in profile as not cold when
profile-sample-accurate is enabled. This caused 70k size regression in
Chrome/Android. The patch put a guard and only enable the change when
profile symbol list is available, i.e., keep the old behavior when profile
symbol list is not available.

Differential Revision: https://reviews.llvm.org/D67931

llvm-svn: 372665