Provide baseline for experimental GC implementation.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 1df9b4750ce53451187ee56ad2197ddfb856b9b3..662b1c432bd9bae8720b2346caf358b0f3eb27bf 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -73,7 +73,7 @@ void MacroAssembler::CompareRoot(Operand with, Heap::RootListIndex index) {
   cmpq(with, kScratchRegister);
 }
 
-
+#ifdef ENABLE_CARDMARKING_WRITE_BARRIER
 void MacroAssembler::RecordWriteHelper(Register object,
                                        Register addr,
                                        Register scratch) {
@@ -214,6 +214,7 @@ void MacroAssembler::RecordWriteNonSmi(Register object,
     movq(index, BitCast<int64_t>(kZapValue), RelocInfo::NONE);
   }
 }
+#endif
 
 void MacroAssembler::Assert(Condition cc, const char* msg) {
   if (FLAG_debug_code) Check(cc, msg);