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 433fc6deab3e0efc7cb921501d7757d1c42a2688..d22f6d268db27ded38e9d468afd739a57233e6e5 100644
--- a/src/heap/objects-visiting-inl.h
+++ b/src/heap/objects-visiting-inl.h
@@ -537,11 +537,6 @@ void StaticMarkingVisitor<StaticVisitor>::VisitJSDataView(Map* map,
 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
@@ -571,23 +566,6 @@ void StaticMarkingVisitor<StaticVisitor>::MarkMapContents(Heap* heap,
 
 
 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));
-  }
-}
-
-
-template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::MarkInlinedFunctionsCode(Heap* heap,
                                                                    Code* code) {
   // For optimized functions we should retain both non-optimized version