Make View::Paint use ui::PaintRecorder to access PaintContext's canvas

ui/compositor/paint_recorder.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 UI_COMPOSITOR_PAINT_RECORDER_H_
+#define UI_COMPOSITOR_PAINT_RECORDER_H_
+
+#include "base/macros.h"
+#include "ui/compositor/compositor_export.h"
+
+namespace gfx {
+class Canvas;
+}
+
+namespace ui {
+class PaintContext;
+
+// A class to hide the complexity behind setting up a recording into a
+// DisplayItem. This is meant to be short-lived within the scope of recording
+// taking place, the DisplayItem should be removed from the PaintRecorder once
+// recording is complete and can be cached.
+class COMPOSITOR_EXPORT PaintRecorder {
+ public:
+  explicit PaintRecorder(const PaintContext& context);
+  ~PaintRecorder();
+
+  // Gets a gfx::Canvas for painting into.
+  gfx::Canvas* canvas() { return canvas_; }
+
+ private:
+  gfx::Canvas* canvas_;
+
+  DISALLOW_COPY_AND_ASSIGN(PaintRecorder);
+};
+
+}  // namespace ui
+
+#endif  // UI_COMPOSITOR_PAINT_RECORDER_H_