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

ash/wm/dock/docked_window_layout_manager.cc

Index: ash/wm/dock/docked_window_layout_manager.cc
diff --git a/ash/wm/dock/docked_window_layout_manager.cc b/ash/wm/dock/docked_window_layout_manager.cc
index dbf6d55c38e18bb912ecf4c851a6bdc0a40d450e..9945fa57556e34e6e0f5eaf9f42ed078fa2db95f 100644
--- a/ash/wm/dock/docked_window_layout_manager.cc
+++ b/ash/wm/dock/docked_window_layout_manager.cc
@@ -31,6 +31,7 @@
 #include "ui/aura/window_delegate.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/base/resource/resource_bundle.h"
+#include "ui/compositor/paint_context.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/geometry/rect.h"
@@ -92,7 +93,8 @@ class DockedBackgroundWidget : public views::Widget,
     UpdateBackground();
   }
 
-  void OnNativeWidgetPaint(gfx::Canvas* canvas) override {
+  void OnNativeWidgetPaint(const ui::PaintContext& context) override {
+    gfx::Canvas* canvas = context.canvas();
     const gfx::ImageSkia& shelf_background(
         alignment_ == DOCKED_ALIGNMENT_LEFT ?
             shelf_background_left_ : shelf_background_right_);