ui/gfx: Make gfx::Canvas inherit from gfx::CanvasSkia.

ui/aura/window_delegate.h

Index: ui/aura/window_delegate.h
diff --git a/ui/aura/window_delegate.h b/ui/aura/window_delegate.h
index 6247b89c9d1a1fe5426130f29338112fca5c058a..2d992c76656093ae7893d11d19fd41794cab816a 100644
--- a/ui/aura/window_delegate.h
+++ b/ui/aura/window_delegate.h
@@ -11,7 +11,7 @@
 #include "ui/gfx/native_widget_types.h"
 
 namespace gfx {
-class Canvas;
+class CanvasSkia;
 class Point;
 class Rect;
 class Size;
@@ -62,7 +62,7 @@ class AURA_EXPORT WindowDelegate {
   virtual void OnCaptureLost() = 0;
 
   // Asks the delegate to paint window contents into the supplied canvas.
-  virtual void OnPaint(gfx::Canvas* canvas) = 0;
+  virtual void OnPaint(gfx::CanvasSkia* canvas) = 0;
 
   // Called from Window's destructor before OnWindowDestroyed and before the
   // children have been destroyed and the window has been removed from its