Count ArrayBuffer's backing_store memory in heap snapshot.

test/cctest/test-heap-profiler.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2363 matching lines @@
   const v8::HeapGraphNode* global = GetGlobalObject(snapshot);
   const v8::HeapGraphNode* arr1_obj =
       GetProperty(global, v8::HeapGraphEdge::kProperty, "arr1");
   CHECK_NE(NULL, arr1_obj);
   const v8::HeapGraphNode* arr1_buffer =
       GetProperty(arr1_obj, v8::HeapGraphEdge::kInternal, "buffer");
   CHECK_NE(NULL, arr1_buffer);
   const v8::HeapGraphNode* first_view =
       GetProperty(arr1_buffer, v8::HeapGraphEdge::kWeak, "weak_first_view");
   CHECK_NE(NULL, first_view);
+  const v8::HeapGraphNode* backing_store =
+      GetProperty(arr1_buffer, v8::HeapGraphEdge::kInternal, "backing_store");
+  CHECK_NE(NULL, backing_store);
+  CHECK_EQ(400, backing_store->GetSelfSize());
 }
 
 
 TEST(BoxObject) {
   v8::Isolate* isolate = CcTest::isolate();
   v8::HandleScope scope(isolate);
   LocalContext env;
   v8::Handle<v8::Object> global_proxy = env->Global();
   v8::Handle<v8::Object> global = global_proxy->GetPrototype().As<v8::Object>();
 
@@ skipping 10 matching lines @@
   const v8::HeapGraphNode* global_node = GetGlobalObject(snapshot);
   const v8::HeapGraphNode* box_node =
       GetProperty(global_node, v8::HeapGraphEdge::kElement, "0");
   CHECK_NE(NULL, box_node);
   v8::String::Utf8Value box_node_name(box_node->GetName());
   CHECK_EQ("system / Box", *box_node_name);
   const v8::HeapGraphNode* box_value =
       GetProperty(box_node, v8::HeapGraphEdge::kInternal, "value");
   CHECK_NE(NULL, box_value);
 }