Use an allocation site scratchpad to speed up allocaton site processing during gc.

src/objects.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 8120 matching lines @@
 
   inline void Initialize();
 
   // This method is expensive, it should only be called for reporting.
   bool IsNestedSite();
 
   class ElementsKindBits:       public BitField<ElementsKind, 0,  15> {};
   class UnusedBits:             public BitField<int,          15, 14> {};
   class DoNotInlineBit:         public BitField<bool,         29,  1> {};
 
-  inline void IncrementMementoFoundCount();
+  // Increments the mementos found counter and returns true when the first
+  // memento was found for a given allocation site.
+  inline bool IncrementMementoFoundCount();
 
   inline void IncrementMementoCreateCount();
 
   PretenureFlag GetPretenureMode() {
     int mode = pretenure_decision()->value();
     // Zombie objects "decide" to be untenured.
     return (mode == kTenure) ? TENURED : NOT_TENURED;
   }
 
   // The pretenuring decision is made during gc, and the zombie state allows
@@ skipping 2465 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_