Ensure that executable pages are properly guarded.

src/spaces-inl.h

Index: src/spaces-inl.h
diff --git a/src/spaces-inl.h b/src/spaces-inl.h
index d0cddebf787de98cc1171b57eeaf8d125a28f102..3709009c9b011357a57ef263aa40f0926da45125 100644
--- a/src/spaces-inl.h
+++ b/src/spaces-inl.h
@@ -166,10 +166,8 @@ Page* Page::Initialize(Heap* heap,
   Page* page = reinterpret_cast<Page*>(chunk);
   ASSERT(chunk->size() == static_cast<size_t>(kPageSize));
   ASSERT(chunk->owner() == owner);
-  owner->IncreaseCapacity(Page::kObjectAreaSize);
-  owner->Free(page->ObjectAreaStart(),
-              static_cast<int>(page->ObjectAreaEnd() -
-                               page->ObjectAreaStart()));
+  owner->IncreaseCapacity(page->area_size());
+  owner->Free(page->area_start(), page->area_size());
 
   heap->incremental_marking()->SetOldSpacePageFlags(chunk);