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

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index e78a45ef5bfe3415688dec93b46aa3c2189fffa8..8893d8cecb882b782c41be0374127d1c0474b3fd 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -1180,12 +1180,12 @@ bool Widget::OnNativeWidgetPaintAccelerated(const gfx::Rect& dirty_region) {
   return true;
 }
 
-void Widget::OnNativeWidgetPaint(gfx::Canvas* canvas) {
+void Widget::OnNativeWidgetPaint(const ui::PaintContext& context) {
   // On Linux Aura, we can get here during Init() because of the
   // SetInitialBounds call.
   if (!native_widget_initialized_)
     return;
-  GetRootView()->Paint(ui::PaintContext(canvas, GetLayer()->PaintRect()));
+  GetRootView()->Paint(context);
 }
 
 int Widget::GetNonClientComponent(const gfx::Point& point) {