Fix LoadFieldByIndex to take mutable heap-numbers into account.

src/arm64/lithium-codegen-arm64.h

Index: src/arm64/lithium-codegen-arm64.h
diff --git a/src/arm64/lithium-codegen-arm64.h b/src/arm64/lithium-codegen-arm64.h
index b1d8b70d5beb09171a5cb2be10d12bc21cc719bc..e06f05cf413d54bc1d65d60754524ec151c76e42 100644
--- a/src/arm64/lithium-codegen-arm64.h
+++ b/src/arm64/lithium-codegen-arm64.h
@@ -149,6 +149,10 @@ class LCodeGen: public LCodeGenBase {
   void DoDeferredAllocate(LAllocate* instr);
   void DoDeferredInstanceOfKnownGlobal(LInstanceOfKnownGlobal* instr);
   void DoDeferredInstanceMigration(LCheckMaps* instr, Register object);
+  void DoDeferredLoadMutableDouble(LLoadFieldByIndex* instr,
+                                   Register result,
+                                   Register object,
+                                   Register index);
 
   Operand ToOperand32(LOperand* op, IntegerSignedness signedness);