Introduce a flag for tracing retaining path in GC.

src/heap/mark-compact.h

 // Copyright 2012 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.
 
 #ifndef V8_HEAP_MARK_COMPACT_H_
 #define V8_HEAP_MARK_COMPACT_H_
 
 #include "src/base/bits.h"
 #include "src/heap/spaces.h"
 
@@ skipping 117 matching lines @@
       to_mark_bit.Next().Set();
       is_black = false;  // Was actually gray.
     }
     return is_black;
   }
 
  private:
   Heap* heap_;
 };
 
+
 // ----------------------------------------------------------------------------
 // Marking deque for tracing live objects.
 class MarkingDeque {
  public:
   MarkingDeque()
       : array_(NULL), top_(0), bottom_(0), mask_(0), overflowed_(false) {}
 
   void Initialize(Address low, Address high) {
     HeapObject** obj_low = reinterpret_cast<HeapObject**>(low);
     HeapObject** obj_high = reinterpret_cast<HeapObject**>(high);
@@ skipping 12 matching lines @@
   bool overflowed() const { return overflowed_; }
 
   void ClearOverflowed() { overflowed_ = false; }
 
   void SetOverflowed() { overflowed_ = true; }
 
   // Push the (marked) object on the marking stack if there is room,
   // otherwise mark the object as overflowed and wait for a rescan of the
   // heap.
   INLINE(void PushBlack(HeapObject* object)) {
+#ifdef TRACE_RETAINING_PATH
+    AddRetainedObject(object);
+#endif
     DCHECK(object->IsHeapObject());
     // TODO(jochen): Remove again before we branch for 4.2.
     CHECK(object->IsHeapObject() && object->map()->IsMap());
     if (IsFull()) {
       Marking::BlackToGrey(object);
       MemoryChunk::IncrementLiveBytesFromGC(object->address(), -object->Size());
       SetOverflowed();
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
     }
   }
 
   INLINE(void PushGrey(HeapObject* object)) {
+#ifdef TRACE_RETAINING_PATH
+    AddRetainedObject(object);
+#endif
     DCHECK(object->IsHeapObject());
     // TODO(jochen): Remove again before we branch for 4.2.
     CHECK(object->IsHeapObject() && object->map()->IsMap());
     if (IsFull()) {
       SetOverflowed();
     } else {
       array_[top_] = object;
       top_ = ((top_ + 1) & mask_);
     }
   }
@@ skipping 16 matching lines @@
     }
   }
 
   HeapObject** array() { return array_; }
   int bottom() { return bottom_; }
   int top() { return top_; }
   int mask() { return mask_; }
   void set_top(int top) { top_ = top; }
 
  private:
+#ifdef TRACE_RETAINING_PATH
+  static void AddRetainedObject(HeapObject* obj);
+#endif
+
   HeapObject** array_;
   // array_[(top - 1) & mask_] is the top element in the deque.  The Deque is
   // empty when top_ == bottom_.  It is full when top_ + 1 == bottom
   // (mod mask + 1).
   int top_;
   int bottom_;
   int mask_;
   bool overflowed_;
 
   DISALLOW_COPY_AND_ASSIGN(MarkingDeque);
@@ skipping 731 matching lines @@
  private:
   MarkCompactCollector* collector_;
 };
 
 
 const char* AllocationSpaceName(AllocationSpace space);
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_MARK_COMPACT_H_