Make it possible to custom-paint without an Element.

sky/engine/core/painting/PaintingContext.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 "sky/engine/config.h"
 #include "sky/engine/core/painting/PaintingContext.h"
 
 #include "sky/engine/core/dom/Document.h"
 #include "sky/engine/core/dom/Element.h"
 #include "sky/engine/core/painting/PaintingTasks.h"
 #include "sky/engine/platform/geometry/IntRect.h"
-#include "third_party/skia/include/core/SkCanvas.h"
 
 namespace blink {
 
 PassRefPtr<PaintingContext> PaintingContext::create(PassRefPtr<Element> element, const FloatSize& size)
 {
     return adoptRef(new PaintingContext(element, size));
 }
 
 PaintingContext::PaintingContext(PassRefPtr<Element> element, const FloatSize& size)
-    : m_element(element)
-    , m_size(size)
+    : Canvas(size)
+    , m_element(element)
 {
-    m_displayList = adoptRef(new DisplayList);
-    m_canvas = m_displayList->beginRecording(expandedIntSize(m_size));
 }
 
 PaintingContext::~PaintingContext()
 {
 }
 
-void PaintingContext::drawCircle(double x, double y, double radius, Paint* paint)
-{
-    if (!m_canvas)
-        return;
-    ASSERT(paint);
-    ASSERT(m_displayList->isRecording());
-    m_canvas->drawCircle(x, y, radius, paint->paint());
-}
-
 void PaintingContext::commit()
 {
-    if (!m_canvas)
+    if (!isRecording())
         return;
-    m_displayList->endRecording();
-    m_canvas = nullptr;
-    PaintingTasks::enqueueCommit(m_element, m_displayList.release());
+    PaintingTasks::enqueueCommit(m_element, finishRecording());
     m_element->document().scheduleVisualUpdate();
 }
 
 } // namespace blink