Faster moving FixedArray elements around.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 3c26dc8990558fb286c50e098c43c0388866082c..2b9321c6890c4e8bc8fe0c22a9734d784037bca0 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -1626,6 +1626,9 @@ class FixedArray: public Array {
   inline void set_null(int index);
   inline void set_the_hole(int index);
 
+  // Gives access to raw memory which stores the array's data.
+  inline Object** data_start();
+
   // Copy operations.
   inline Object* Copy();
   Object* CopySize(int new_length);