Just clear semi-space mark bits once before Scavenge

src/heap/incremental-marking.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/heap/incremental-marking.h"
 
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 560 matching lines @@
        FLAG_max_object_groups_marking_rounds) ||
       (marking_progress < FLAG_min_progress_during_object_groups_marking)) {
     weak_closure_was_overapproximated_ = true;
   }
 
   heap_->isolate()->global_handles()->RemoveImplicitRefGroups();
   heap_->isolate()->global_handles()->RemoveObjectGroups();
 }
 
 
-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;
 
   MarkingDeque* marking_deque =
       heap_->mark_compact_collector()->marking_deque();
   int current = marking_deque->bottom();
   int mask = marking_deque->mask();
   int limit = marking_deque->top();
   HeapObject** array = marking_deque->array();
   int new_top = current;
@@ skipping 434 matching lines @@
 void IncrementalMarking::IncrementIdleMarkingDelayCounter() {
   idle_marking_delay_counter_++;
 }
 
 
 void IncrementalMarking::ClearIdleMarkingDelayCounter() {
   idle_marking_delay_counter_ = 0;
 }
 }
 }  // namespace v8::internal