Fix assert in PagedSpace::SizeOfObject for concurrent sweeping.

src/spaces.h

Index: src/spaces.h
diff --git a/src/spaces.h b/src/spaces.h
index e7e11db55f7e9de7c91342e13f6268a74454514e..fe22341308f029dd8dd15128f0c7682056b8630e 100644
--- a/src/spaces.h
+++ b/src/spaces.h
@@ -1648,11 +1648,7 @@ class PagedSpace : public Space {
 
   // As size, but the bytes in lazily swept pages are estimated and the bytes
   // in the current linear allocation area are not included.
-  virtual intptr_t SizeOfObjects() {
-    // TODO(hpayer): broken when concurrent sweeping turned on
-    ASSERT(!IsLazySweepingComplete() || (unswept_free_bytes_ == 0));
-    return Size() - unswept_free_bytes_ - (limit() - top());
-  }
+  virtual intptr_t SizeOfObjects();
 
   // Wasted bytes in this space.  These are just the bytes that were thrown away
   // due to being too small to use for allocation.  They do not include the