First implementation of fast path for instantiation of array literals composed of doubles.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c7093a817bfc46bb939701f7a63497de22a1261d..1525057026be7fbca53654d8eb206b5a7d835550 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2340,6 +2340,7 @@ class FixedDoubleArray: public FixedArrayBase {
  public:
   // Setter and getter for elements.
   inline double get_scalar(int index);
+  inline int64_t get_representation(int index);
   MUST_USE_RESULT inline MaybeObject* get(int index);
   inline void set(int index, double value);
   inline void set_the_hole(int index);