Just clear semi-space mark bits once before Scavenge

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 d8e07aaab9b07b2650f922f1399e039314389ae5..4c070423603c190dc6dc7c4e77e128a9d55cf525 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -578,16 +578,6 @@ void IncrementalMarking::MarkObjectGroups() {
 }
 
 
-void IncrementalMarking::PrepareForScavenge() {
-  if (!IsMarking()) return;
-  NewSpacePageIterator it(heap_->new_space()->FromSpaceStart(),
-                          heap_->new_space()->FromSpaceEnd());
-  while (it.has_next()) {
-    Bitmap::Clear(it.next());
-  }
-}
-
-
 void IncrementalMarking::UpdateMarkingDequeAfterScavenge() {
   if (!IsMarking()) return;