[heap] Pass a force_promotion flag to the evacuation routine in the scavenger.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 12ae76583d35d72870a155eb85d4762eef5af202..82642266af2a04577c2ee3905a8e682db66d2d3c 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -301,7 +301,10 @@ class Scavenger;
 class ScavengeJob;
 class WeakObjectRetainer;
 
-typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to);
+enum PromotionMode { FORCE_PROMOTION, DEFAULT_PROMOTION };
+
+typedef void (*ObjectSlotCallback)(HeapObject** from, HeapObject* to,
+                                   PromotionMode mode);
 
 // A queue of objects promoted during scavenge. Each object is accompanied
 // by it's size to avoid dereferencing a map pointer for scanning.