Add rendering context and rendering 2D context to OffscreenCanvas

third_party/WebKit/Source/core/html/canvas/OffscreenCanvas.cpp

-// 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.
-
-#include "core/html/canvas/OffscreenCanvas.h"
-
-#include "wtf/MathExtras.h"
-
-namespace blink {
-
-OffscreenCanvas* OffscreenCanvas::create(unsigned width, unsigned height)
-{
-    return new OffscreenCanvas(IntSize(clampTo<int>(width), clampTo<int>(height)));
-}
-
-void OffscreenCanvas::setWidth(unsigned width)
-{
-    m_size.setWidth(clampTo<int>(width));
-}
-
-void OffscreenCanvas::setHeight(unsigned height)
-{
-    m_size.setHeight(clampTo<int>(height));
-}
-
-OffscreenCanvas::OffscreenCanvas(const IntSize& size)
-    : m_size(size)
-{
-}
-
-DEFINE_TRACE(OffscreenCanvas)
-{
-}
-
-} // namespace blink