ui: Use a PaintRecorder to access the Canvas for painting.

ui/aura/demo/demo_main.cc

Index: ui/aura/demo/demo_main.cc
diff --git a/ui/aura/demo/demo_main.cc b/ui/aura/demo/demo_main.cc
index bf23d451f9892b5376b671ed398e54b65b4cec22..52a09d3d7b1fc45ffc8aed760a7ca329c0214fc0 100644
--- a/ui/aura/demo/demo_main.cc
+++ b/ui/aura/demo/demo_main.cc
@@ -19,7 +19,7 @@
 #include "ui/aura/window_delegate.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/hit_test.h"
-#include "ui/compositor/paint_context.h"
+#include "ui/compositor/paint_recorder.h"
 #include "ui/compositor/test/in_process_context_factory.h"
 #include "ui/events/event.h"
 #include "ui/gfx/canvas.h"
@@ -64,15 +64,15 @@ class DemoWindowDelegate : public aura::WindowDelegate {
   bool CanFocus() override { return true; }
   void OnCaptureLost() override {}
   void OnPaint(const ui::PaintContext& context) override {
-    gfx::Canvas* canvas = context.canvas();
-    canvas->DrawColor(color_, SkXfermode::kSrc_Mode);
+    ui::PaintRecorder recorder(context);
+    recorder.canvas()->DrawColor(color_, SkXfermode::kSrc_Mode);
     gfx::Rect r;
-    canvas->GetClipBounds(&r);
+    recorder.canvas()->GetClipBounds(&r);
     // Fill with a non-solid color so that the compositor will exercise its
     // texture upload path.
     while (!r.IsEmpty()) {
       r.Inset(2, 2);
-      canvas->FillRect(r, color_, SkXfermode::kXor_Mode);
+      recorder.canvas()->FillRect(r, color_, SkXfermode::kXor_Mode);
     }
   }
   void OnDeviceScaleFactorChanged(float device_scale_factor) override {}