[turbofan] Use sorted set in JSInliningHeuristic.

src/compiler/js-inlining-heuristic.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_JS_INLINING_HEURISTIC_H_
 #define V8_COMPILER_JS_INLINING_HEURISTIC_H_
 
 #include "src/compiler/js-inlining.h"
 
 namespace v8 {
@@ skipping 19 matching lines @@
   // and inlines call sites that the heuristic determines to be important.
   void ProcessCandidates();
 
  private:
   struct Candidate {
     Handle<JSFunction> function;  // The call target being inlined.
     Node* node;                   // The call site at which to inline.
     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_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_INLINING_HEURISTIC_H_