components: Move PrefRegistrySyncable into user_prefs namespace.

chrome/browser/prefs/incognito_mode_prefs.h

Index: chrome/browser/prefs/incognito_mode_prefs.h
diff --git a/chrome/browser/prefs/incognito_mode_prefs.h b/chrome/browser/prefs/incognito_mode_prefs.h
index cbd35faf11e6059aa8fcb278021a197b53281dca..791e8655ce02a914477da5db2a831b112a1fce1e 100644
--- a/chrome/browser/prefs/incognito_mode_prefs.h
+++ b/chrome/browser/prefs/incognito_mode_prefs.h
@@ -9,7 +9,10 @@
 
 class CommandLine;
 class PrefService;
+
+namespace user_prefs {
 class PrefRegistrySyncable;
+}
 
 // Specifies Incognito mode availability preferences.
 class IncognitoModePrefs {
@@ -31,7 +34,7 @@ class IncognitoModePrefs {
   };
 
   // Register incognito related preferences.
-  static void RegisterUserPrefs(PrefRegistrySyncable* registry);
+  static void RegisterUserPrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // Returns kIncognitoModeAvailability preference value stored
   // in the given pref service.