Tweak compaction candidate selection to avoid keeping page with low occupancy around.

src/mark-compact.h

Index: src/mark-compact.h
diff --git a/src/mark-compact.h b/src/mark-compact.h
index a911b49d2ee25f46989221f968defc6da8c60c98..135f22043549e3ae34aed2cc437f895c6bcef0c8 100644
--- a/src/mark-compact.h
+++ b/src/mark-compact.h
@@ -374,7 +374,7 @@ class SlotsBuffer {
   static const int kNumberOfElements = 1021;
 
  private:
-  static const int kChainLengthThreshold = 6;
+  static const int kChainLengthThreshold = 15;
 
   intptr_t idx_;
   intptr_t chain_length_;
@@ -572,6 +572,8 @@ class MarkCompactCollector {
   // heap.
   bool sweep_precisely_;
 
+  bool reduce_memory_footprint_;
+
   // True if we are collecting slots to perform evacuation from evacuation
   // candidates.
   bool compacting_;