Incremental mode now works for x64. The only difference

src/arm/code-stubs-arm.h

Index: src/arm/code-stubs-arm.h
===================================================================
--- src/arm/code-stubs-arm.h	(revision 8221)
+++ src/arm/code-stubs-arm.h	(working copy)
@@ -533,7 +533,17 @@
     friend class RecordWriteStub;
   };
 
+  enum OnNoNeedToInformIncrementalMarker {
+    kReturnOnNoNeedToInformIncrementalMarker,
+    kRememberedSetOnNoNeedToInformIncrementalMarker
+  };
+
   void Generate(MacroAssembler* masm);
+  void GenerateIncremental(MacroAssembler* masm);
+  void CheckNeedsToInformIncrementalMarker(
+      MacroAssembler* masm,
+      OnNoNeedToInformIncrementalMarker on_no_need);
+  void InformIncrementalMarker(MacroAssembler* masm);
 
   Major MajorKey() { return RecordWrite; }