If customization includes default wallpaper, download and apply it.

ash/shell/shell_delegate_impl.h

Index: ash/shell/shell_delegate_impl.h
diff --git a/ash/shell/shell_delegate_impl.h b/ash/shell/shell_delegate_impl.h
index 2b5aa12b223dce38225bd824f4f3b0d4ac76cb6d..5631b5781f74d2220fadc91e43ff3b2916777580 100644
--- a/ash/shell/shell_delegate_impl.h
+++ b/ash/shell/shell_delegate_impl.h
@@ -59,6 +59,11 @@ class ShellDelegateImpl : public ash::ShellDelegate {
   virtual WindowTreeHostFactory* CreateWindowTreeHostFactory() OVERRIDE;
   virtual GPUSupport* CreateGPUSupport() OVERRIDE;
   virtual base::string16 GetProductName() const OVERRIDE;
+  virtual bool ShouldUseCustomizedDefaultWallpaper() const OVERRIDE;
+  virtual base::FilePath GetCustomizedWallpaperDefaultRescaledSmallFileName()
+      const OVERRIDE;
+  virtual base::FilePath GetCustomizedWallpaperDefaultRescaledLargeFileName()
+      const OVERRIDE;
 
  private:
   // Used to update Launcher. Owned by main.