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

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index b41a8d350503f38a588e18bbdaa92404099c3023..88838e73efe3727cc34b929509466571e45bcc55 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -1380,9 +1380,12 @@ inline DependentCode::DependencyGroup AllocationSite::ToDependencyGroup(
 }
 
 
-inline void AllocationSite::IncrementMementoFoundCount() {
+inline bool AllocationSite::IncrementMementoFoundCount() {
+  if (IsZombie()) return false;
+
   int value = memento_found_count()->value();
   set_memento_found_count(Smi::FromInt(value + 1));
+  return value == 0;
 }