Reset user data directory and disk cache directory after downgrade.

chrome/browser/policy/policy_path_parser_mac.mm

Index: chrome/browser/policy/policy_path_parser_mac.mm
diff --git a/chrome/browser/policy/policy_path_parser_mac.mm b/chrome/browser/policy/policy_path_parser_mac.mm
index 24275f68069f59e89970ed295fa7fc6bdb300dd3..a6a565b03f1f2615069469b6f51d953b35b18e2b 100644
--- a/chrome/browser/policy/policy_path_parser_mac.mm
+++ b/chrome/browser/policy/policy_path_parser_mac.mm
@@ -114,6 +114,12 @@ void CheckUserDataDirPolicy(base::FilePath* user_data_dir) {
   }
 }
 
+void CheckDiskCacheDirPolicy(base::FilePath* user_data_dir) {
+  // This function is not implemented in Mac because it's only used by the
+  // feature in Windows.
+  NOTREACHED();
+}
+
 }  // namespace path_parser
 
 }  // namespace policy