Avoid manual object's body traversal in GC.

src/objects.cc

 // Copyright 2013 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 1985 matching lines @@
       os << "<Other heap object (" << map()->instance_type() << ")>";
       break;
   }
 }
 
 
 void HeapObject::Iterate(ObjectVisitor* v) {
   // Handle header
   IteratePointer(v, kMapOffset);
   // Handle object body
+  IterateBody(v);
+}
+
+
+void HeapObject::IterateBody(ObjectVisitor* v) {
   Map* m = map();
   IterateBody(m->instance_type(), SizeFromMap(m), v);
 }
 
 
 bool HeapNumber::HeapNumberBooleanValue() {
   return DoubleToBoolean(value());
 }
 
 
@@ skipping 15885 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8