This CL fixes a long-lasting bug that prevented pprof from recognizing
Legacy heap profile produced by Go. Go reports four types of samples
at once so the profile includes alloc_objects, alloc_space,
inuse_objects, and inuse_space. The bug caused pprof to misclassify Go
heap profile data and prevent selection of correct filtering/pruning
patterns in analysis.

Update golang/go#25096

Tested with the profile samples included in golang.org/issues/25096
(pprof hides the runtime functions with this change)