[heap] Fix verification of counters

No-Try: true
Bug: v8:6845
Change-Id: Ic823fe62e0ee6a954ca704d37a6cb54473720b9c
Reviewed-on: https://chromium-review.googlesource.com/676890
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48104}

src/heap/spaces.cc

@@ -1769,6 +1769,11 @@ void PagedSpace::VerifyCountersAfterSweeping() {
 }
 
 void PagedSpace::VerifyCountersBeforeConcurrentSweeping() {
+  // We need to refine the counters on pages that are already swept and have
+  // not been moved over to the actual space. Otherwise, the AccountingStats
+  // are just an over approximation.
+  RefillFreeList();
+
   size_t total_capacity = 0;
   size_t total_allocated = 0;
   auto marking_state =