Ensure that executable pages are properly guarded.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index bb5c37562e1c6ff16ed010509b7b2afc04309114..e2fee0c1d5b7d7ae2178d044cdd4ae686ad18ff7 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -345,7 +345,7 @@ class PromotionQueue {
           NewSpacePage::FromAddress(reinterpret_cast<Address>(front_));
       ASSERT(!front_page->prev_page()->is_anchor());
       front_ =
-          reinterpret_cast<intptr_t*>(front_page->prev_page()->body_limit());
+          reinterpret_cast<intptr_t*>(front_page->prev_page()->area_end());
     }
     *target = reinterpret_cast<HeapObject*>(*(--front_));
     *size = static_cast<int>(*(--front_));
@@ -484,9 +484,6 @@ class Heap {
   // all available bytes. Check MaxHeapObjectSize() instead.
   intptr_t Available();
 
-  // Returns the maximum object size in paged space.
-  inline int MaxObjectSizeInPagedSpace();
-
   // Returns of size of all objects residing in the heap.
   intptr_t SizeOfObjects();