Remove usages of Heap::NewSpaceStart and its external reference

src/heap/spaces.cc

 // 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.
 
 #include "src/heap/spaces.h"
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
 #include "src/full-codegen/full-codegen.h"
 #include "src/heap/slot-set.h"
@@ skipping 1317 matching lines @@
 
   to_space_.SetUp(chunk_base_, initial_semispace_capacity,
                   maximum_semispace_capacity);
   from_space_.SetUp(chunk_base_ + reserved_semispace_capacity,
                     initial_semispace_capacity, maximum_semispace_capacity);
   if (!to_space_.Commit()) {
     return false;
   }
   DCHECK(!from_space_.is_committed());  // No need to use memory yet.
 
-  start_ = chunk_base_;
-
   ResetAllocationInfo();
 
   return true;
 }
 
 
 void NewSpace::TearDown() {
   if (allocated_histogram_) {
     DeleteArray(allocated_histogram_);
     allocated_histogram_ = NULL;
   }
   if (promoted_histogram_) {
     DeleteArray(promoted_histogram_);
     promoted_histogram_ = NULL;
   }
 
-  start_ = NULL;
   allocation_info_.Reset(nullptr, nullptr);
 
-
   to_space_.TearDown();
   from_space_.TearDown();
 
   heap()->isolate()->memory_allocator()->FreeNewSpaceMemory(
       chunk_base_, &reservation_, NOT_EXECUTABLE);
 
   chunk_base_ = NULL;
   chunk_size_ = 0;
 }
 
@@ skipping 1791 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8