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

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index d2d69618934f3eb7799423a1ecec2941ce750bd3..31660dd6ac962fd59bb86882ea6a8b5fd1397e7a 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -2057,6 +2057,11 @@ class Heap {
   void GarbageCollectionPrologue();
   void GarbageCollectionEpilogue();
 
+  // Pretenuring decisions are made based on feedback collected during new
+  // space evacuation. Note that between feedback collection and calling this
+  // method object in old space must not move.
+  void ProcessPretenuringFeedback();
+
   // Checks whether a global GC is necessary
   GarbageCollector SelectGarbageCollector(AllocationSpace space,
                                           const char** reason);
@@ -2383,6 +2388,11 @@ class Heap {
   int no_weak_object_verification_scope_depth_;
 #endif
 
+
+  static const int kAllocationSiteScratchpadSize = 256;
+  int allocation_sites_scratchpad_length;
+  AllocationSite* allocation_sites_scratchpad[kAllocationSiteScratchpadSize];
+
   static const int kMaxMarkSweepsInIdleRound = 7;
   static const int kIdleScavengeThreshold = 5;