When adjusting page's live bytes counter from the mutator adjust owners unswept free bytes counter.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index dc61949d19406faef903219d363884c9ec06bdfb..f49873ac4ffb5303b9b7227391625105ea623368 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -472,10 +472,13 @@ class MemoryChunk {
     ASSERT(static_cast<unsigned>(live_byte_count_) <= size_);
     return live_byte_count_;
   }
-  static void IncrementLiveBytes(Address address, int by) {
+
+  static void IncrementLiveBytesFromGC(Address address, int by) {
     MemoryChunk::FromAddress(address)->IncrementLiveBytes(by);
   }
 
+  static void IncrementLiveBytesFromMutator(Address address, int by);
+
   static const intptr_t kAlignment =
       (static_cast<uintptr_t>(1) << kPageSizeBits);
 
@@ -1563,6 +1566,10 @@ class PagedSpace : public Space {
     first_unswept_page_ = first;
   }
 
+  void IncrementUnsweptFreeBytes(int by) {
+    unswept_free_bytes_ += by;
+  }
+
   void IncreaseUnsweptFreeBytes(Page* p) {
     ASSERT(ShouldBeSweptLazily(p));
     unswept_free_bytes_ += (Page::kObjectAreaSize - p->LiveBytes());