use SkSurface behind gfx::Canvas

ui/gfx/canvas.h

 // Copyright (c) 2012 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_GFX_CANVAS_H_
 #define UI_GFX_CANVAS_H_
 
 #include <stdint.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "skia/ext/platform_canvas.h"
-#include "third_party/skia/include/core/SkRefCnt.h"
+#include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkSurface.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/gfx/shadow_value.h"
 #include "ui/gfx/text_constants.h"
-
 namespace gfx {
 
 class Rect;
 class RectF;
 class FontList;
 class Point;
 class PointF;
 class Size;
 class Transform;
 
@@ skipping 467 matching lines @@
                           bool filter,
                           const SkPaint& paint,
                           bool remove_image_scale);
 
   // The device scale factor at which drawing on this canvas occurs.
   // An additional scale can be applied via Canvas::Scale(). However,
   // Canvas::Scale() does not affect |image_scale_|.
   float image_scale_;
 
   // canvas_ is our active canvas object. Sometimes we are also the owner,
-  // in which case canvas_owner_ will be set. Other times we are just
+  // in which case surface_ will be set. Other times we are just
   // borrowing someone else's canvas, in which case canvas_ will point there
-  // but canvas_owner_ will be null.
-  std::unique_ptr<SkCanvas> canvas_owner_;
+  // but surface_ will be null.
+  sk_sp<SkSurface> surface_;
   SkCanvas* canvas_;
 
   DISALLOW_COPY_AND_ASSIGN(Canvas);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_CANVAS_H_