Introduce PaintingContext, which will be used for custom painting

sky/engine/core/painting/PaintingContext.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 SKY_ENGINE_CORE_PAINTING_PAINTINGCONTEXT_H_
+#define SKY_ENGINE_CORE_PAINTING_PAINTINGCONTEXT_H_
+
+#include "sky/engine/core/painting/Paint.h"
+#include "sky/engine/platform/graphics/DisplayList.h"
+#include "sky/engine/tonic/dart_wrappable.h"
+#include "sky/engine/wtf/PassRefPtr.h"
+#include "sky/engine/wtf/RefCounted.h"
+
+namespace blink {
+
+class PaintingContext : public RefCounted<PaintingContext>, public DartWrappable {
+    DEFINE_WRAPPERTYPEINFO();
+public:
+    ~PaintingContext() override;
+    PassRefPtr<PaintingContext> create(const FloatRect& bounds) { return adoptRef(new PaintingContext(bounds)); }
+
+    double height() const { return m_displayList->bounds().height(); }
+    double width() const { return m_displayList->bounds().width(); }
+
+    void drawCircle(double x, double y, double radius, Paint* paint);
+    void commit();
+
+private:
+    PaintingContext(const FloatRect& bounds);
+
+    RefPtr<DisplayList> m_displayList;
+    SkCanvas* m_canvas;
+};
+
+} // namespace blink
+
+#endif  // SKY_ENGINE_CORE_PAINTING_PAINTINGCONTEXT_H_