[turbofan] Use sorted set in JSInliningHeuristic.

src/compiler/js-inlining-heuristic.h

Index: src/compiler/js-inlining-heuristic.h
diff --git a/src/compiler/js-inlining-heuristic.h b/src/compiler/js-inlining-heuristic.h
index a4a0ec3b75855a1c197cf27771b943f0800eadb6..c6f04be0455521243b812c11b5412968064e9e8e 100644
--- a/src/compiler/js-inlining-heuristic.h
+++ b/src/compiler/js-inlining-heuristic.h
@@ -37,14 +37,22 @@ class JSInliningHeuristic final : public AdvancedReducer {
     int calls;                    // Number of times the call site was hit.
   };
 
-  static bool Compare(const Candidate& left, const Candidate& right);
+  // Comparator for candidates.
+  struct CandidateCompare {
+    bool operator()(const Candidate& left, const Candidate& right) const;
+  };
+
+  // Candidates are kept in a sorted set of unique candidates.
+  typedef ZoneSet<Candidate, CandidateCompare> Candidates;
+
+  // Dumps candidates to console.
   void PrintCandidates();
 
   Mode const mode_;
   Zone* local_zone_;
   JSGraph* jsgraph_;
   JSInliner inliner_;
-  ZoneVector<Candidate> candidates_;
+  Candidates candidates_;
   CompilationInfo* info_;
 };