[heap] Check that sweeping is completed when collecting evacuation

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 1a85216e3ff6ce84299081d8bbe3414b6f2a1319..81122da6213bec889b403be6180bbd21d043b46c 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -638,6 +638,9 @@ void MarkCompactCollector::CollectEvacuationCandidates(PagedSpace* space) {
   std::vector<LiveBytesPagePair> pages;
   pages.reserve(number_of_pages);
 
+  DCHECK(!sweeping_in_progress());
+  DCHECK(!FLAG_concurrent_sweeping ||
+         sweeper().IsSweepingCompleted(space->identity()));
   for (Page* p : *space) {
     if (p->NeverEvacuate()) continue;
     // Invariant: Evacuation candidates are just created when marking is