If customization includes default wallpaper, download and apply it.

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index ba28e0ca26cf941c3737507dac9193f368272067..ae08f4ddac1a6061edcdc1644662e15acaf58fc8 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -133,6 +133,17 @@ class ASH_EXPORT ShellDelegate {
 
   // Get the product name.
   virtual base::string16 GetProductName() const = 0;
+
+  // If device should use customized default wallpaper.
+  virtual bool ShouldUseCustomizedDefaultWallpaper() const = 0;
+
+  // Returns small scale customized wallpaper file name.
+  virtual base::FilePath GetCustomizedWallpaperDefaultRescaledSmallFileName()
+      const = 0;
+
+  // Returns large scale customized wallpaper file name.
+  virtual base::FilePath GetCustomizedWallpaperDefaultRescaledLargeFileName()
+      const = 0;
 };
 
 }  // namespace ash