bindings: Adds DOMArrayBuffer, etc. as thin wrappers for ArrayBuffer, etc.

Source/core/dom/DOMArrayBufferDeallocationObserver.cpp

+// Copyright 2014 The Chromium 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 "config.h"
+#include "core/dom/DOMArrayBufferDeallocationObserver.h"
+
+#include "wtf/StdLibExtras.h"
+#include <v8.h>
+
+namespace blink {
+
+DOMArrayBufferDeallocationObserver* DOMArrayBufferDeallocationObserver::instance()
+{
+    DEFINE_STATIC_LOCAL(DOMArrayBufferDeallocationObserver, deallocationObserver, ());
+    return &deallocationObserver;
+}
+
+void DOMArrayBufferDeallocationObserver::arrayBufferDeallocated(unsigned sizeInBytes)
+{
+    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(-static_cast<int>(sizeInBytes));

[haraken, 2014/10/14 15:11:19]

If possible, we want to pass |isolate| to this method and avoid calling
v8::Isolate::GetCurrent(). You can address this in a follow-up CL.

[Yuki, 2014/10/15 09:35:23]

It seems very hard.  These are callback functions and wtf::ArrayBufferContents's
dtor and clear() method calls these callback.

One idea is that we create DOMArrayBufferDeallocationObserver for each isolate,
and make the observer remember the isolate.  However, the observer is expected
permanent lifetime by ArrayBufferContents and it makes the things difficult
(isolate doesn't have permanent lifetime).

I have several options here in my mind, but all the options make the code
complicated (e.g. lifetime management of observers, isolate -> observer
mapping).

+}
+
+void DOMArrayBufferDeallocationObserver::blinkAllocatedMemory(unsigned sizeInBytes)
+{
+    v8::Isolate::GetCurrent()->AdjustAmountOfExternalAllocatedMemory(static_cast<int>(sizeInBytes));

[haraken, 2014/10/14 15:11:19]

Ditto.

+}
+
+} // namespace blink