Add language_prefs namespace to language_preferences.h.

chrome/browser/chromeos/login/language_switch_menu.cc

Index: chrome/browser/chromeos/login/language_switch_menu.cc
diff --git a/chrome/browser/chromeos/login/language_switch_menu.cc b/chrome/browser/chromeos/login/language_switch_menu.cc
index 884583b51ec1120db3f46fa7af508d3bf4432321..0c3521bf97e982d8262e3c6353177788de15adbc 100644
--- a/chrome/browser/chromeos/login/language_switch_menu.cc
+++ b/chrome/browser/chromeos/login/language_switch_menu.cc
@@ -99,9 +99,9 @@ void LanguageSwitchMenu::SwitchLanguage(const std::string& locale) {
     ResourceBundle::ReloadSharedInstance(locale);
 
     // Enable the keyboard layouts that are necessary for the new locale.
-    chromeos::input_method::EnableInputMethods(
-        locale, chromeos::input_method::kKeyboardLayoutsOnly,
-        kHardwareKeyboardLayout);
+    input_method::EnableInputMethods(
+        locale, input_method::kKeyboardLayoutsOnly,
+        language_prefs::kHardwareKeyboardLayout);
 
     // The following line does not seem to affect locale anyhow. Maybe in
     // future..