heap: Consider embedder objects when linearly processing ephemerons

Without the proper check V8 would not delegate to the embedder (Blink) for
processing wrappable objects.

Bug: chromium:946941
Change-Id: I5aa3ca85e5113ab8d28a61eca6a5e0593c62f6a1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1547649
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60545}

src/heap/mark-compact.cc

@@ -1645,6 +1645,7 @@ void MarkCompactCollector::ProcessEphemeronsLinear() {
     // is necessary.
 
     work_to_do = !marking_worklist()->IsEmpty() ||
+                 !marking_worklist()->IsEmbedderEmpty() ||
                  !heap()->local_embedder_heap_tracer()->IsRemoteTracingDone();
     CHECK(weak_objects_.discovered_ephemerons.IsEmpty());
   }