Pass a ui::PaintContext from ui::Layer to layer delegates.

ui/views/widget/widget_unittest.cc

Index: ui/views/widget/widget_unittest.cc
diff --git a/ui/views/widget/widget_unittest.cc b/ui/views/widget/widget_unittest.cc
index e3265493c042fe458e63f8d3d19130f2273dc823..1c5f67b8dc4ce2953ad32b3289a4ab64a94f7d69 100644
--- a/ui/views/widget/widget_unittest.cc
+++ b/ui/views/widget/widget_unittest.cc
@@ -1299,12 +1299,12 @@ class DesktopAuraTestValidPaintWidget : public views::Widget {
     views::Widget::Hide();
   }
 
-  void OnNativeWidgetPaint(gfx::Canvas* canvas) override {
+  void OnNativeWidgetPaint(const ui::PaintContext& context) override {
     received_paint_ = true;
     EXPECT_TRUE(expect_paint_);
     if (!expect_paint_)
       received_paint_while_hidden_ = true;
-    views::Widget::OnNativeWidgetPaint(canvas);
+    views::Widget::OnNativeWidgetPaint(context);
   }
 
   bool ReadReceivedPaintAndReset() {