Enable user change background image in settings page in Aura build.

ash/desktop_background/desktop_background_view.h

Index: ash/desktop_background/desktop_background_view.h
diff --git a/ash/desktop_background/desktop_background_view.h b/ash/desktop_background/desktop_background_view.h
index 6af658325a6423f13ad9e61ed3b0852a91ba986c..ec67634b62d4410b5790dad292d7b524f667b5cc 100644
--- a/ash/desktop_background/desktop_background_view.h
+++ b/ash/desktop_background/desktop_background_view.h
@@ -6,19 +6,25 @@
 #define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_VIEW_H_
 #pragma once
 
+#include "base/memory/singleton.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/views/view.h"
 #include "ui/views/widget/widget_delegate.h"
 
 namespace ash {
+

[flackr, 2012/03/05 16:16:03]

nit: no newline here.

[bshe, 2012/03/06 01:33:27]

Done.

 namespace internal {
 
 class DesktopBackgroundView : public views::WidgetDelegateView {
  public:
   DesktopBackgroundView();
   virtual ~DesktopBackgroundView();
+  void SetWallpaper(const SkBitmap& wallpaper);
+  static DesktopBackgroundView* GetInstance();
 
  private:
+  friend struct DefaultSingletonTraits<DesktopBackgroundView>;

[flackr, 2012/03/05 16:16:03]

I worry about the implications of making this class a Singleton. This class
doesn't have to exist if BackgroundMode is BACKGROUND_SOLID_COLOR and things may
get trickier if eventually there are more than one RootWindow. I think you
should be modifying Shell::SetDesktopBackgroundMode or making a new function in
ash::Shell for setting the desktop background. Since ash::Shell creates the
desktop backgrounds it can remember the DesktopBackgroundView or just create a
new one when you set a new wallpaper.

[bshe, 2012/03/06 01:33:27]

I created a new function called SetDesktopBackgroundWallpaper in shell.

+
   // Overridden from views::View:
   virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE;
   virtual bool OnMousePressed(const views::MouseEvent& event) OVERRIDE;