Add ManagedUserSettingsService and a SupervisedUserPrefStore using it.

chrome/chrome_tests_unit.gypi

Index: chrome/chrome_tests_unit.gypi
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index 957dd28d84e92b9662d6f9afb7d738eb9d891335..e01de446c01e3df42da77584de0ae795cc42f449 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -1098,6 +1098,7 @@
         'browser/prefs/chrome_pref_service_unittest.cc',
         'browser/prefs/command_line_pref_store_unittest.cc',
         'browser/prefs/incognito_mode_prefs_unittest.cc',
+        'browser/prefs/supervised_user_pref_store_unittest.cc',
         'browser/prefs/pref_model_associator_unittest.cc',
         'browser/prefs/proxy_config_dictionary_unittest.cc',
         'browser/prefs/proxy_policy_unittest.cc',
@@ -2629,6 +2630,9 @@
           'sources/': [
             ['exclude', '^browser/managed_mode/'],
           ],
+          'sources!': [
+            'browser/prefs/supervised_user_pref_store_unittest.cc',
+          ],
         }],
         ['safe_browsing!=1', {
           'sources/': [