If a large object is truncated, also truncate the page.

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 "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/ring_buffer.h"
@@ skipping 278 matching lines @@
     kGCTimeFraction = 1,
     kPageGrowth = 2,
     kAllowedGrowth = 3
   };
 
   static const intptr_t kAllocatablePageSize = 64 * KB;
 
   HeapPage* AllocatePage(HeapPage::PageType type);
   void FreePage(HeapPage* page, HeapPage* previous_page);
   HeapPage* AllocateLargePage(intptr_t size, HeapPage::PageType type);
+  void TruncateLargePage(HeapPage* page, intptr_t new_object_size_in_bytes);
   void FreeLargePage(HeapPage* page, HeapPage* previous_page);
   void FreePages(HeapPage* pages);
   HeapPage* NextPageAnySize(HeapPage* page) const {
     ASSERT(pages_tail_ == NULL || pages_tail_->next() == NULL);
     return page == pages_tail_ ? large_pages_ : page->next();
   }
 
   static intptr_t LargePageSizeInWordsFor(intptr_t size);
 
   bool CanIncreaseCapacityInWords(intptr_t increase_in_words) {
@@ skipping 22 matching lines @@
   intptr_t collections_;
 
   friend class PageSpaceController;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_