[NOT FOR LANDING] Patch for experiments: V8

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index fd58ef06a08f78fca205de119a38453bb51f3249..f7e8afbe801182553ba9d2ee0e82adfe4577c73c 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -736,15 +736,10 @@ void IncrementalMarking::FinalizeIncrementally() {
   // 4) Remove weak cell with live values from the list of weak cells, they
   // do not need processing during GC.
   MarkRoots();
-  if (!heap_->local_embedder_heap_tracer()->InUse()) {
+  if (!heap_->local_embedder_heap_tracer()->InUse() &&
+      FLAG_object_grouping_in_incremental_finalization) {
     MarkObjectGroups();
   }
-  if (incremental_marking_finalization_rounds_ == 0) {

[ulan, 2017/03/30 16:24:30]

This changes reduce noise in incremental finalization step.

-    // Map retaining is needed for perfromance, not correctness,
-    // so we can do it only once at the beginning of the finalization.
-    RetainMaps();
-  }
-  ProcessWeakCells();
 
   int marking_progress =
       abs(old_marking_deque_top -