If customization includes default wallpaper, download and apply it.

ash/test/test_shell_delegate.cc

Index: ash/test/test_shell_delegate.cc
diff --git a/ash/test/test_shell_delegate.cc b/ash/test/test_shell_delegate.cc
index 57c76cc097e2cbd06c5f21b55bdc9ea3f06369c2..f8cdaf069ebfda429c58ff1835694dd07b76f6e0 100644
--- a/ash/test/test_shell_delegate.cc
+++ b/ash/test/test_shell_delegate.cc
@@ -155,5 +155,19 @@ TestSessionStateDelegate* TestShellDelegate::test_session_state_delegate() {
   return test_session_state_delegate_;
 }
 
+bool TestShellDelegate::ShouldUseCustomizedDefaultWallpaper() const {
+  return false;
+}
+
+base::FilePath
+TestShellDelegate::GetCustomizedWallpaperDefaultRescaledSmallFileName() const {
+  return base::FilePath();
+}
+
+base::FilePath
+TestShellDelegate::GetCustomizedWallpaperDefaultRescaledLargeFileName() const {
+  return base::FilePath();
+}
+
 }  // namespace test
 }  // namespace ash