message: libc++ fix: make comparison functors const
diff: @@ -138,7 +138,7 @@ class GraphAnalyzer {
  // The entries are owned by collation_map_, so must be removed from
  // ordered_collation_ before removing them from collation_map_.
  struct ReverseLessByCount {
  - bool operator()(CollationEntry* left, CollationEntry* right) {
  + bool operator()(CollationEntry* left, CollationEntry* right) const {
  return left->count > right->count; // Reverse order.
  }
  };
  