[Tracing] Use TracingCategoryObserver in gc statistics

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>
 #include <map>
 
@@ skipping 926 matching lines @@
   bool ConfigureHeapDefault();
 
   // Prepares the heap, setting up memory areas that are needed in the isolate
   // without actually creating any objects.
   bool SetUp();
 
   // Bootstraps the object heap with the core set of objects required to run.
   // Returns whether it succeeded.
   bool CreateHeapObjects();
 
+  // Create ObjectStats if live_object_stats_ or dead_object_stats_ are nullptr.
+  V8_INLINE void CreateObjectStats();
+
   // Destroys all memory allocated by the heap.
   void TearDown();
 
   // Returns whether SetUp has been called.
   bool HasBeenSetUp();
 
   // ===========================================================================
   // Getters for spaces. =======================================================
   // ===========================================================================
 
@@ skipping 1668 matching lines @@
   friend class LargeObjectSpace;
   friend class NewSpace;
   friend class PagedSpace;
   DISALLOW_COPY_AND_ASSIGN(AllocationObserver);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_HEAP_HEAP_H_