Just clear semi-space mark bits once before Scavenge

src/heap/incremental-marking.h

 // 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.
 
 #ifndef V8_HEAP_INCREMENTAL_MARKING_H_
 #define V8_HEAP_INCREMENTAL_MARKING_H_
 
 
 #include "src/execution.h"
 #include "src/heap/mark-compact.h"
@@ skipping 55 matching lines @@
   bool ShouldActivateEvenWithoutIdleNotification();
 
   bool WasActivated();
 
   void Start(int mark_compact_flags);
 
   void Stop();
 
   void MarkObjectGroups();
 
-  void PrepareForScavenge();
-
   void UpdateMarkingDequeAfterScavenge();
 
   void Hurry();
 
   void Finalize();
 
   void Abort();
 
   void OverApproximateWeakClosure(CompletionAction action);
 
@@ skipping 156 matching lines @@
   int weak_closure_approximation_rounds_;
 
   GCRequestType request_type_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_INCREMENTAL_MARKING_H_