Re-land new insertion write barrier.

src/heap/spaces.h

 // Copyright 2011 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_SPACES_H_
 #define V8_HEAP_SPACES_H_
 
 #include "src/allocation.h"
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
@@ skipping 490 matching lines @@
     progress_bar_ = progress_bar;
   }
 
   void ResetProgressBar() {
     if (IsFlagSet(MemoryChunk::HAS_PROGRESS_BAR)) {
       set_progress_bar(0);
       ClearFlag(MemoryChunk::HAS_PROGRESS_BAR);
     }
   }
 
-  bool IsLeftOfProgressBar(Object** slot) {
-    Address slot_address = reinterpret_cast<Address>(slot);
-    DCHECK(slot_address > this->address());
-    return (slot_address - (this->address() + kObjectStartOffset)) <
-           progress_bar();
-  }
-
   static void IncrementLiveBytesFromGC(Address address, int by) {
     MemoryChunk::FromAddress(address)->IncrementLiveBytes(by);
   }
 
   static void IncrementLiveBytesFromMutator(Address address, int by);
 
   static const intptr_t kAlignment =
       (static_cast<uintptr_t>(1) << kPageSizeBits);
 
   static const intptr_t kAlignmentMask = kAlignment - 1;
@@ skipping 2357 matching lines @@
     count = 0;
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_SPACES_H_