Add a base::Feature for the pref service.

chrome/common/chrome_features.cc

Index: chrome/common/chrome_features.cc
diff --git a/chrome/common/chrome_features.cc b/chrome/common/chrome_features.cc
index 62e7eb1b2afb9409945d6879dc4ce9e532e10d8b..5b0ceda3f8b4a3876502a7f790237e24162884b1 100644
--- a/chrome/common/chrome_features.cc
+++ b/chrome/common/chrome_features.cc
@@ -215,6 +215,10 @@ const base::Feature kPreferHtmlOverPlugins{"PreferHtmlOverPlugins",
                                            base::FEATURE_DISABLED_BY_DEFAULT};
 #endif
 
+// Enables the pref service. See https://crbug.com/654988.
+const base::Feature kPrefService{"PrefService",
+                                 base::FEATURE_DISABLED_BY_DEFAULT};
+
 #if defined(OS_CHROMEOS)
 // The lock screen will be preloaded so it is instantly available when the user
 // locks the Chromebook device.