Faster moving FixedArray elements around.

src/heap-inl.h

Index: src/heap-inl.h
diff --git a/src/heap-inl.h b/src/heap-inl.h
index f18bf0f61b69b6811cfe9844477993e29d54b71c..1acdb2a081be9e6196ac99c991c7a0fa0aa3fee0 100644
--- a/src/heap-inl.h
+++ b/src/heap-inl.h
@@ -187,6 +187,18 @@ void Heap::RecordWrite(Address address, int offset) {
 }
 
 
+void Heap::RecordWrites(Address address, int start, int len) {
+  if (new_space_.Contains(address)) return;
+  ASSERT(!new_space_.FromSpaceContains(address));
+  for (int offset = start;
+       offset < start + len * kPointerSize;
+       offset += kPointerSize) {
+    SLOW_ASSERT(Contains(address + offset));
+    Page::SetRSet(address, offset);
+  }
+}
+
+
 OldSpace* Heap::TargetSpace(HeapObject* object) {
   InstanceType type = object->map()->instance_type();
   AllocationSpace space = TargetSpaceId(type);