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

ui/views/widget/native_widget_win.h

Index: ui/views/widget/native_widget_win.h
diff --git a/ui/views/widget/native_widget_win.h b/ui/views/widget/native_widget_win.h
index a3537c7356730ccb96de30bf07da12ed8b4dbac8..eb3d6d189233db7678f33d422a2c729340ab47e5 100644
--- a/ui/views/widget/native_widget_win.h
+++ b/ui/views/widget/native_widget_win.h
@@ -32,7 +32,7 @@ class ViewProp;
 }
 
 namespace gfx {
-class CanvasSkia;
+class Canvas;
 class Font;
 class Rect;
 }
@@ -550,7 +550,7 @@ class VIEWS_EXPORT NativeWidgetWin : public ui::WindowImpl,
 
   // A canvas that contains the window contents in the case of a layered
   // window.
-  scoped_ptr<gfx::CanvasSkia> layered_window_contents_;
+  scoped_ptr<gfx::Canvas> layered_window_contents_;
 
   // We must track the invalid rect ourselves, for two reasons:
   // For layered windows, Windows will not do this properly with