ui: Introduce CanvasPainter, remove PaintContext(gfx::Canvas*).

ui/compositor/canvas_painter.cc

+// 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 "ui/compositor/canvas_painter.h"
+
+#include "cc/playback/display_item_list.h"
+#include "cc/playback/display_item_list_settings.h"
+#include "ui/gfx/canvas.h"
+
+namespace ui {
+
+CanvasPainter::CanvasPainter(gfx::Canvas* canvas, float raster_scale_factor)
+    : canvas_(canvas),
+      raster_scale_factor_(raster_scale_factor),
+      rect_(gfx::ScaleToEnclosedRect(
+          gfx::Rect(canvas_->sk_canvas()->getBaseLayerSize().width(),
+                    canvas_->sk_canvas()->getBaseLayerSize().height()),
+          1.f / raster_scale_factor)),
+      list_(cc::DisplayItemList::Create(rect_, cc::DisplayItemListSettings())),
+      context_(list_.get(), raster_scale_factor_, rect_, rect_) {
+}
+
+CanvasPainter::~CanvasPainter() {
+  list_->Finalize();
+  list_->Raster(canvas_->sk_canvas(), nullptr, rect_, raster_scale_factor_);
+}
+
+}  // namespace ui