Log Message:
gperftools 2.6 is out!

* Kim Gräsman contributed documentation update for HEAPPROFILESIGNAL
  environment variable

* KernelMaker contributed fix for population of min_object_size field
  returned by MallocExtension::GetFreeListSizes

* commit 8c3dc52fcfe0 "issue-654: [pprof] handle split text segments"
  was reverted. Some OSX users reported issues with this commit. Given
  our pprof implementation is strongly deprecated it is best to drop
  recently introduced features rather than breaking it badly.