Fix bug introduced by r21269.

runtime/vm/pages.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_PAGES_H_
 #define VM_PAGES_H_
 
 #include <map>
 
 #include "vm/freelist.h"
@@ skipping 17 matching lines @@
   };
 
   HeapPage* next() const { return next_; }
   void set_next(HeapPage* next) { next_ = next; }
 
   bool Contains(uword addr) {
     return memory_->Contains(addr);
   }
 
   uword object_start() const {
-    return (reinterpret_cast<uword>(this) +
-            Utils::RoundUp(sizeof(HeapPage), OS::kMaxPreferredCodeAlignment));
+    return (reinterpret_cast<uword>(this) + ObjectStartOffset());
   }
   uword object_end() const {
     return object_end_;
   }
 
   void set_used(uword used) { used_ = used; }
   uword used() const { return used_; }
   void AddUsed(uword size) {
     used_ += size;
   }
 
   PageType type() const {
     return executable_ ? kExecutable : kData;
   }
 
   void VisitObjects(ObjectVisitor* visitor) const;
   void VisitObjectPointers(ObjectPointerVisitor* visitor) const;
 
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
   void WriteProtect(bool read_only);
 
+  static intptr_t ObjectStartOffset() {
+    return Utils::RoundUp(sizeof(HeapPage), OS::kMaxPreferredCodeAlignment);
+  }
+
  private:
   void set_object_end(uword val) {
     ASSERT((val & kObjectAlignmentMask) == kOldObjectAlignmentOffset);
     object_end_ = val;
   }
 
   static HeapPage* Initialize(VirtualMemory* memory, PageType type);
   static HeapPage* Allocate(intptr_t size, PageType type);
 
   // Deallocate the virtual memory backing this page. The page pointer to this
@@ skipping 206 matching lines @@
   PageSpaceController page_space_controller_;
 
   friend class PageSpaceController;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_