[printing] Add COW identifier to elements kind

src/objects-printer.cc

 // 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.
 
 #include "src/objects.h"
 
 #include "src/disasm.h"
 #include "src/disassembler.h"
 #include "src/interpreter/bytecodes.h"
 #include "src/objects-inl.h"
@@ skipping 378 matching lines @@
       break;
   }
 }
 
 
 static void JSObjectPrintHeader(std::ostream& os, JSObject* obj,
                                 const char* id) {  // NOLINT
   obj->PrintHeader(os, id);
   // Don't call GetElementsKind, its validation code can cause the printer to
   // fail when debugging.
+  os << "\n - map = " << reinterpret_cast<void*>(obj->map()) << " ["
+     << ElementsKindToString(obj->map()->elements_kind());
+  if (obj->elements()->map() == obj->GetHeap()->fixed_cow_array_map()) {
+    os << " (COW)";
+  }
   PrototypeIterator iter(obj->GetIsolate(), obj);
-  os << "\n - map = " << reinterpret_cast<void*>(obj->map()) << " ["
-     << ElementsKindToString(obj->map()->elements_kind())
-     << "]\n - prototype = " << reinterpret_cast<void*>(iter.GetCurrent());
+  os << "]\n - prototype = " << reinterpret_cast<void*>(iter.GetCurrent());
+  if (obj->elements()->length() > 0) {
+    os << "\n - elements = " << Brief(obj->elements());
+  }
 }
 
 
 static void JSObjectPrintBody(std::ostream& os, JSObject* obj,  // NOLINT
                               bool print_elements = true) {
   os << "\n {";
   obj->PrintProperties(os);
   obj->PrintTransitions(os);
   if (print_elements) obj->PrintElements(os);
   os << "\n }\n";
@@ skipping 917 matching lines @@
 void JSObject::PrintTransitions(std::ostream& os) {  // NOLINT
   Object* transitions = map()->raw_transitions();
   int num_transitions = TransitionArray::NumberOfTransitions(transitions);
   if (num_transitions == 0) return;
   os << "\n - transitions";
   TransitionArray::PrintTransitions(os, transitions, false);
 }
 #endif  // defined(DEBUG) || defined(OBJECT_PRINT)
 }  // namespace internal
 }  // namespace v8