If customization includes default wallpaper, download and apply it.

ash/test/test_shell_delegate.h

Index: ash/test/test_shell_delegate.h
diff --git a/ash/test/test_shell_delegate.h b/ash/test/test_shell_delegate.h
index a41d1bb1948d75e7926236deb14b06066fdff320..d183a9031c2cf41f3bbed3cf849d75b6a1798a78 100644
--- a/ash/test/test_shell_delegate.h
+++ b/ash/test/test_shell_delegate.h
@@ -55,6 +55,11 @@ class TestShellDelegate : public 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;
 
   int num_exit_requests() const { return num_exit_requests_; }