[heap] Use HashMap as scratchpad backing store

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 8129 matching lines @@
   class DoNotInlineBit:         public BitField<bool,         29,  1> {};
 
   // Bitfields for pretenure_data
   class MementoFoundCountBits:  public BitField<int,               0, 26> {};
   class PretenureDecisionBits:  public BitField<PretenureDecision, 26, 3> {};
   class DeoptDependentCodeBit:  public BitField<bool,              29, 1> {};
   STATIC_ASSERT(PretenureDecisionBits::kMax >= kLastPretenureDecisionValue);
 
   // Increments the mementos found counter and returns true when the first
   // memento was found for a given allocation site.
-  inline bool IncrementMementoFoundCount();
+  inline bool IncrementMementoFoundCount(int increment = 1);
 
   inline void IncrementMementoCreateCount();
 
   PretenureFlag GetPretenureMode();
 
   void ResetPretenureDecision();
 
   inline PretenureDecision pretenure_decision();
   inline void set_pretenure_decision(PretenureDecision decision);
 
@@ skipping 2576 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_