Fix bogus assert in HeapIterator.

src/store-buffer.cc

Index: src/store-buffer.cc
diff --git a/src/store-buffer.cc b/src/store-buffer.cc
index dbd9cc7415e04b47bf57f3aedf8143ff3dfb9930..34835f0ee03844a1df2ab187dc078cfabb117b3c 100644
--- a/src/store-buffer.cc
+++ b/src/store-buffer.cc
@@ -505,9 +505,9 @@ void StoreBuffer::IteratePointersToNewSpace(ObjectSlotCallback slot_callback,
               }
             }
           } else {
-            if (page->parallel_sweeping() > MemoryChunk::SWEEPING_FINALIZE) {
+            if (!page->SweepingCompleted()) {
               heap_->mark_compact_collector()->SweepInParallel(page, owner);
-              if (page->parallel_sweeping() > MemoryChunk::SWEEPING_FINALIZE) {
+              if (!page->SweepingCompleted()) {
                 // We were not able to sweep that page, i.e., a concurrent
                 // sweeper thread currently owns this page.
                 // TODO(hpayer): This may introduce a huge pause here. We