Update the app banner action button to display "add" by default.

chrome/browser/banners/app_banner_settings_helper.cc

Index: chrome/browser/banners/app_banner_settings_helper.cc
diff --git a/chrome/browser/banners/app_banner_settings_helper.cc b/chrome/browser/banners/app_banner_settings_helper.cc
index 2898939505149379e8381e3ca499f0e0f23250d2..a795a6c245ca98929104589f2caa37a4f6c7f7dd 100644
--- a/chrome/browser/banners/app_banner_settings_helper.cc
+++ b/chrome/browser/banners/app_banner_settings_helper.cc
@@ -401,7 +401,7 @@ AppBannerSettingsHelper::GetHomescreenLanguageOption() {
   if (param.empty() || !base::StringToUint(param, &language_option) ||
       language_option < LANGUAGE_OPTION_MIN ||
       language_option > LANGUAGE_OPTION_MAX) {
-    return LANGUAGE_OPTION_DEFAULT;
+    return LANGUAGE_OPTION_ADD;
   }
 
   return static_cast<LanguageOption>(language_option);