Implement setting the length of FixedDoubleArrays.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 43747cc8fa1b6ffef0b698aaaf2c329f54399be3..9b55ea747545799a7f35aa4948bdcfad46dccd0b 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2169,6 +2169,9 @@ class FixedDoubleArray: public FixedArrayBase {
     return kHeaderSize + length * kDoubleSize;
   }
 
+  // Code Generation support.
+  static int OffsetOfElementAt(int index) { return SizeFor(index); }
+
   inline static bool is_the_hole_nan(double value);
   inline static double hole_nan_as_double();
   inline static double canonical_not_the_hole_nan_as_double();