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

ui/snapshot/snapshot_aura_unittest.cc

Index: ui/snapshot/snapshot_aura_unittest.cc
diff --git a/ui/snapshot/snapshot_aura_unittest.cc b/ui/snapshot/snapshot_aura_unittest.cc
index b15a5807b6b20aa5cb0c49012caa1879e679b84a..c134ca08aba37d43b78ffc485927b8fbe2628532 100644
--- a/ui/snapshot/snapshot_aura_unittest.cc
+++ b/ui/snapshot/snapshot_aura_unittest.cc
@@ -15,6 +15,7 @@
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/compositor/compositor.h"
 #include "ui/compositor/layer.h"
+#include "ui/compositor/paint_context.h"
 #include "ui/compositor/test/context_factories_for_test.h"
 #include "ui/compositor/test/draw_waiter_for_test.h"
 #include "ui/gfx/canvas.h"
@@ -42,10 +43,12 @@ class TestPaintingWindowDelegate : public aura::test::TestWindowDelegate {
 
   ~TestPaintingWindowDelegate() override {}
 
-  void OnPaint(gfx::Canvas* canvas) override {
+  void OnPaint(const ui::PaintContext& context) override {
     for (int y = 0; y < window_size_.height(); ++y) {
-      for (int x = 0; x < window_size_.width(); ++x)
-        canvas->FillRect(gfx::Rect(x, y, 1, 1), GetExpectedColorForPoint(x, y));
+      for (int x = 0; x < window_size_.width(); ++x) {
+        context.canvas()->FillRect(gfx::Rect(x, y, 1, 1),
+                                   GetExpectedColorForPoint(x, y));
+      }
     }
   }