Shrinking of PagedSpace is done only by sweeper.

src/spaces.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1680 matching lines @@
     accounting_stats_.AllocateBytes(bytes);
   }
 
   void IncreaseCapacity(int size) {
     accounting_stats_.ExpandSpace(size);
   }
 
   // Releases an unused page and shrinks the space.
   void ReleasePage(Page* page);
 
-  // Releases all of the unused pages.
-  void ReleaseAllUnusedPages();
-
   // The dummy page that anchors the linked list of pages.
   Page* anchor() { return &anchor_; }
 
 #ifdef VERIFY_HEAP
   // Verify integrity of this space.
   virtual void Verify(ObjectVisitor* visitor);
 
   // Overridden by subclasses to verify space-specific object
   // properties (e.g., only maps or free-list nodes are in map space).
   virtual void VerifyObject(HeapObject* obj) {}
@@ skipping 1107 matching lines @@
   }
   // Must be small, since an iteration is used for lookup.
   static const int kMaxComments = 64;
 };
 #endif
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SPACES_H_