Introduce a flag for tracing retaining path in GC.

src/heap/heap.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_HEAP_H_
 #define V8_HEAP_HEAP_H_
 
 #include <cmath>
 
+#ifdef TRACE_RETAINING_PATH
+#include <map>
+#include <string>
+#endif
+
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/counters.h"
 #include "src/globals.h"
 #include "src/heap/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/incremental-marking.h"
 #include "src/heap/mark-compact.h"
 #include "src/heap/objects-visiting.h"
 #include "src/heap/spaces.h"
@@ skipping 1417 matching lines @@
   // trigger the event. In order to track ALL allocations one must turn off
   // FLAG_inline_new and FLAG_use_allocation_folding.
   inline void OnAllocationEvent(HeapObject* object, int size_in_bytes);
 
   // This event is triggered after object is moved to a new place.
   inline void OnMoveEvent(HeapObject* target, HeapObject* source,
                           int size_in_bytes);
 
   bool deserialization_complete() const { return deserialization_complete_; }
 
+#ifdef TRACE_RETAINING_PATH
+  void SetCurrentRetainer(HeapObject* obj);
+  void SetCurrentRootRetainer(std::string root);
+  void AddRetainedObject(HeapObject* obj);
+#endif
+
  protected:
   // Methods made available to tests.
 
   // Allocates a JS Map in the heap.
   MUST_USE_RESULT AllocationResult
       AllocateMap(InstanceType instance_type, int instance_size,
                   ElementsKind elements_kind = TERMINAL_FAST_ELEMENTS_KIND);
 
   // Allocates and initializes a new JavaScript object based on a
   // constructor.
@@ skipping 660 matching lines @@
   VisitorDispatchTable<ScavengingCallback> scavenging_visitors_table_;
 
   MemoryChunk* chunks_queued_for_free_;
 
   base::Mutex relocation_mutex_;
 
   int gc_callbacks_depth_;
 
   bool deserialization_complete_;
 
+#ifdef TRACE_RETAINING_PATH
+  void ClearRetainingInfo();
+  void PrintRetainingPath(HeapObject* obj, const char* comment);
+  std::map<HeapObject*, HeapObject*> retainer_;
+  std::map<HeapObject*, std::string> root_retainer_;
+  HeapObject* current_retainer_;
+  std::string current_root_retainer_;
+#endif
+
   friend class AlwaysAllocateScope;
   friend class Deserializer;
   friend class Factory;
   friend class GCCallbacksScope;
   friend class GCTracer;
   friend class HeapIterator;
   friend class Isolate;
   friend class MarkCompactCollector;
   friend class MarkCompactMarkingVisitor;
   friend class MapCompact;
@@ skipping 448 matching lines @@
   DisallowHeapAllocation no_allocation;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 }
 }  // namespace v8::internal
 
 #endif  // V8_HEAP_HEAP_H_