Introduce FlexibleArrayBufferView and TypedFlexibleArrayBufferView

Source/core/dom/FlexibleArrayBufferView.h

+// Copyright 2015 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.
+
+#ifndef FlexibleArrayBufferView_h
+#define FlexibleArrayBufferView_h
+
+#include "core/CoreExport.h"
+#include "core/dom/DOMArrayBufferView.h"
+#include "platform/heap/Handle.h"
+#include "wtf/Noncopyable.h"
+
+namespace blink {
+
+class CORE_EXPORT FlexibleArrayBufferView {
+    STACK_ALLOCATED();
+    WTF_MAKE_NONCOPYABLE(FlexibleArrayBufferView);
+public:
+    FlexibleArrayBufferView()
+        : m_smallData(nullptr)
+        , m_smallLength(0)
+    {
+    }
+
+    void setFull(DOMArrayBufferView* full) { m_full = full; }
+    void setSmall(void* data, size_t length)
+    {
+        m_smallData = data;
+        m_smallLength = length;
+    }
+
+    void clear()
+    {
+        m_full = nullptr;
+        m_smallData = nullptr;
+        m_smallLength = 0;
+    }
+
+    bool isEmpty() const { return !m_full && !m_smallData; }
+    bool isFull() const { return m_full; }
+
+    DOMArrayBufferView* full() const
+    {
+        ASSERT(isFull());
+        return m_full.get();
+    }
+
+    // WARNING: The pointer returned by baseAddressMaybeOnStack() may point to
+    // temporary storage that is only valid during the life-time of the
+    // FlexibleArrayBufferView object.
+    void* baseAddressMaybeOnStack() const
+    {
+        ASSERT(!isEmpty());
+        return isFull() ? m_full->baseAddress() : m_smallData;
+    }
+
+    unsigned byteOffset() const
+    {
+        ASSERT(!isEmpty());
+        return isFull() ? m_full->byteOffset() : 0;
+    }
+
+    unsigned byteLength() const
+    {
+        ASSERT(!isEmpty());
+        return isFull() ? m_full->byteLength() : m_smallLength;
+    }
+
+    operator bool() const { return !isEmpty(); }
+
+private:
+    RefPtr<DOMArrayBufferView> m_full;
+
+    void* m_smallData;
+    size_t m_smallLength;
+};
+
+} // namespace blink
+
+#endif // FlexibleArrayBufferView_h