Introduce a flag for tracing retaining path in GC.

src/heap/objects-visiting.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/heap/objects-visiting.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 168 matching lines @@
 // We don't record weak slots during marking or scavenges. Instead we do it
 // once when we complete mark-compact cycle.  Note that write barrier has no
 // effect if we are already in the middle of compacting mark-sweep cycle and we
 // have to record slots manually.
 static bool MustRecordSlots(Heap* heap) {
   return heap->gc_state() == Heap::MARK_COMPACT &&
          heap->mark_compact_collector()->is_compacting();
 }
 
 
+#ifdef TRACE_RETAINING_PATH
+void SetCurrentRetainer(HeapObject* obj) {
+  obj->GetHeap()->SetCurrentRetainer(obj);
+}
+
+
+void ResetCurrentRetainer(HeapObject* obj) {
+  obj->GetHeap()->SetCurrentRetainer(NULL);
+}
+#endif
+
 template <class T>
 struct WeakListVisitor;
 
 
 template <class T>
 Object* VisitWeakList(Heap* heap, Object* list, WeakObjectRetainer* retainer) {
   Object* undefined = heap->undefined_value();
   Object* head = undefined;
   T* tail = NULL;
   MarkCompactCollector* collector = heap->mark_compact_collector();
@@ skipping 213 matching lines @@
 
 
 template Object* VisitWeakList<JSArrayBuffer>(Heap* heap, Object* list,
                                               WeakObjectRetainer* retainer);
 
 
 template Object* VisitWeakList<AllocationSite>(Heap* heap, Object* list,
                                                WeakObjectRetainer* retainer);
 }
 }  // namespace v8::internal