[heap] Disable moving object starts aka left trimming

src/heap/heap.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/heap/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/base/bits.h"
 #include "src/base/once.h"
@@ skipping 3682 matching lines @@
     FreeSpace::cast(filler)->nobarrier_set_size(size);
   }
   // At this point, we may be deserializing the heap from a snapshot, and
   // none of the maps have been created yet and are NULL.
   DCHECK((filler->map() == NULL && !deserialization_complete_) ||
          filler->map()->IsMap());
 }
 
 
 bool Heap::CanMoveObjectStart(HeapObject* object) {
+  if (!FLAG_move_object_start) return false;
+
   Address address = object->address();
 
   if (lo_space()->Contains(object)) return false;
 
   Page* page = Page::FromAddress(address);
   // We can move the object start if:
   // (1) the object is not in old space,
   // (2) the page of the object was already swept,
   // (3) the page was already concurrently swept. This case is an optimization
   // for concurrent sweeping. The WasSwept predicate for concurrently swept
@@ skipping 3164 matching lines @@
     *object_type = "CODE_TYPE";                                                \
     *object_sub_type = "CODE_AGE/" #name;                                      \
     return true;
     CODE_AGE_LIST_COMPLETE(COMPARE_AND_RETURN_NAME)
 #undef COMPARE_AND_RETURN_NAME
   }
   return false;
 }
 }  // namespace internal
 }  // namespace v8