Use signaling NaN for holes in fixed double arrays.

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
diff --git a/src/x64/lithium-x64.h b/src/x64/lithium-x64.h
index 8b7a5bc3c90a063ec67e8149115994b65bdbf251..3a07bac96402fca140ae0aa981b7543127702779 100644
--- a/src/x64/lithium-x64.h
+++ b/src/x64/lithium-x64.h
@@ -1319,18 +1319,12 @@ class LConstantS FINAL : public LTemplateInstruction<1, 0, 0> {
 };
 
 
-class LConstantD FINAL : public LTemplateInstruction<1, 0, 1> {
+class LConstantD FINAL : public LTemplateInstruction<1, 0, 0> {
  public:
-  explicit LConstantD(LOperand* temp) {
-    temps_[0] = temp;
-  }
-
-  LOperand* temp() { return temps_[0]; }
-
   DECLARE_CONCRETE_INSTRUCTION(ConstantD, "constant-d")
   DECLARE_HYDROGEN_ACCESSOR(Constant)
 
-  double value() const { return hydrogen()->DoubleValue(); }
+  uint64_t bits() const { return hydrogen()->DoubleValueAsBits(); }
 };