Reland "Merge cellspace into old pointer space"

src/heap/mark-compact.h

Index: src/heap/mark-compact.h
diff --git a/src/heap/mark-compact.h b/src/heap/mark-compact.h
index 2bd53df773d49e3a3f74f96480c0c1eb9a6114e7..29f81ded5a26c356724af5b1efe58af54c4da4e5 100644
--- a/src/heap/mark-compact.h
+++ b/src/heap/mark-compact.h
@@ -319,6 +319,7 @@ class SlotsBuffer {
   enum SlotType {
     EMBEDDED_OBJECT_SLOT,
     RELOCATED_CODE_OBJECT,
+    CELL_TARGET_SLOT,
     CODE_TARGET_SLOT,
     CODE_ENTRY_SLOT,
     DEBUG_TARGET_SLOT,
@@ -332,6 +333,8 @@ class SlotsBuffer {
         return "EMBEDDED_OBJECT_SLOT";
       case RELOCATED_CODE_OBJECT:
         return "RELOCATED_CODE_OBJECT";
+      case CELL_TARGET_SLOT:
+        return "CELL_TARGET_SLOT";
       case CODE_TARGET_SLOT:
         return "CODE_TARGET_SLOT";
       case CODE_ENTRY_SLOT: