Revert of Replace ad-hoc weakness in transition array with WeakCell.

src/heap/objects-visiting-inl.h

Index: src/heap/objects-visiting-inl.h
diff --git a/src/heap/objects-visiting-inl.h b/src/heap/objects-visiting-inl.h
index d22f6d268db27ded38e9d468afd739a57233e6e5..433fc6deab3e0efc7cb921501d7757d1c42a2688 100644
--- a/src/heap/objects-visiting-inl.h
+++ b/src/heap/objects-visiting-inl.h
@@ -537,6 +537,11 @@
 template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::MarkMapContents(Heap* heap,
                                                           Map* map) {
+  Object* raw_transitions = map->raw_transitions();
+  if (TransitionArray::IsFullTransitionArray(raw_transitions)) {
+    MarkTransitionArray(heap, TransitionArray::cast(raw_transitions));
+  }
+
   // Since descriptor arrays are potentially shared, ensure that only the
   // descriptors that belong to this map are marked. The first time a
   // non-empty descriptor array is marked, its header is also visited. The slot
@@ -562,6 +567,23 @@
   StaticVisitor::VisitPointers(
       heap, HeapObject::RawField(map, Map::kPointerFieldsBeginOffset),
       HeapObject::RawField(map, Map::kPointerFieldsEndOffset));
+}
+
+
+template <typename StaticVisitor>
+void StaticMarkingVisitor<StaticVisitor>::MarkTransitionArray(
+    Heap* heap, TransitionArray* transitions) {
+  if (!StaticVisitor::MarkObjectWithoutPush(heap, transitions)) return;
+
+  if (transitions->HasPrototypeTransitions()) {
+    StaticVisitor::VisitPointer(heap,
+                                transitions->GetPrototypeTransitionsSlot());
+  }
+
+  int num_transitions = TransitionArray::NumberOfTransitions(transitions);
+  for (int i = 0; i < num_transitions; ++i) {
+    StaticVisitor::VisitPointer(heap, transitions->GetKeySlot(i));
+  }
 }