IDL: Add [FlexibleArrayBufferView] and use for bufferSubData

Source/core/dom/FlexibleArrayBufferView.h

Index: Source/core/dom/FlexibleArrayBufferView.h
diff --git a/Source/core/dom/FlexibleArrayBufferView.h b/Source/core/dom/FlexibleArrayBufferView.h
new file mode 100644
index 0000000000000000000000000000000000000000..7e4079a562701211acd227a215cb52635704ceeb
--- /dev/null
+++ b/Source/core/dom/FlexibleArrayBufferView.h
@@ -0,0 +1,51 @@
+// 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 {
+
+// WARNING: The pointer returned by baseAddress() may point to temporary storage
+// that is only valid during the life-time of the FlexibleArrayBufferView object.
+
+class CORE_EXPORT FlexibleArrayBufferView {
+    DISALLOW_ALLOCATION();
+    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; }
+
+    bool isEmpty() const { return !m_full && !m_smallData; }
+
+    bool isFull() const { return m_full; }
+    DOMArrayBufferView* full() const { ASSERT(isFull()); return m_full.get(); }
+
+    void* baseAddress() 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(); }
+    void operator= (nullptr_t) { m_full = nullptr; m_smallData = nullptr; }
+
+private:
+    RefPtr<DOMArrayBufferView> m_full;
+
+    void* m_smallData;
+    size_t m_smallLength;
+};
+
+} // namespace blink
+
+#endif // FlexibleArrayBufferView_h