Use signaling NaN for holes in fixed double arrays.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 72df9984dd760e9c6d2ab4ec8926dc1870b7b937..3f485e5dfa334c6aaf1024194c44529721e8320e 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2552,7 +2552,7 @@ class FixedDoubleArray: public FixedArrayBase {
  public:
   // Setter and getter for elements.
   inline double get_scalar(int index);
-  inline int64_t get_representation(int index);
+  inline uint64_t get_representation(int index);
   static inline Handle<Object> get(Handle<FixedDoubleArray> array, int index);
   inline void set(int index, double value);
   inline void set_the_hole(int index);
@@ -2573,10 +2573,6 @@ class FixedDoubleArray: public FixedArrayBase {
   // 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();
-
   DECLARE_CAST(FixedDoubleArray)
 
   // Maximal allowed size, in bytes, of a single FixedDoubleArray.