[heap] Do not trace through blink after making weak roots strong for finalizers

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 400e1e49d66b61f6933efc356fa081df074220e6..42307cd84cf5b2789e136fac80fef789f837d45b 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2140,23 +2140,32 @@ void MarkCompactCollector::ProcessEphemeralMarking(
   DCHECK(marking_deque()->IsEmpty() && !marking_deque()->overflowed());
   bool work_to_do = true;
   while (work_to_do) {
-    if (heap_->UsingEmbedderHeapTracer()) {
-      TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WRAPPER_TRACING);
-      heap_->RegisterWrappersWithEmbedderHeapTracer();
-      heap_->embedder_heap_tracer()->AdvanceTracing(
-          0, EmbedderHeapTracer::AdvanceTracingActions(
-                 EmbedderHeapTracer::ForceCompletionAction::FORCE_COMPLETION));
-    }
     if (!only_process_harmony_weak_collections) {
-      TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_OBJECT_GROUPING);
-      isolate()->global_handles()->IterateObjectGroups(
-          visitor, &IsUnmarkedHeapObjectWithHeap);
-      MarkImplicitRefGroups(&MarkCompactMarkingVisitor::MarkObject);
+      if (heap_->UsingEmbedderHeapTracer()) {
+        TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_WRAPPER_TRACING);
+        heap_->RegisterWrappersWithEmbedderHeapTracer();
+        heap_->embedder_heap_tracer()->AdvanceTracing(
+            0,
+            EmbedderHeapTracer::AdvanceTracingActions(
+                EmbedderHeapTracer::ForceCompletionAction::FORCE_COMPLETION));
+      } else {
+        TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_MARK_OBJECT_GROUPING);
+        isolate()->global_handles()->IterateObjectGroups(
+            visitor, &IsUnmarkedHeapObjectWithHeap);
+        MarkImplicitRefGroups(&MarkCompactMarkingVisitor::MarkObject);
+      }
+    } else {
+      // TODO(mlippautz): We currently do not trace through blink when
+      // discovering new objects reachable from weak roots (that have been made
+      // strong). This is a limitation of not having a separate handle type
+      // that doesn't require zapping before this phase. See crbug.com/668060.
+      heap_->clear_wrappers_to_trace();
     }
     ProcessWeakCollections();
     work_to_do = !marking_deque()->IsEmpty();
     ProcessMarkingDeque<MarkCompactMode::FULL>();
   }
+  CHECK(heap_->MarkingDequesAreEmpty());
 }
 
 void MarkCompactCollector::ProcessTopOptimizedFrame(ObjectVisitor* visitor) {