Add Active Directory login UI tests

chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h
index e2da9b4cc1f19caf9a9c182bddd773d9cd71f3ee..baeee53e445ba0c75ccc8bb64126ff2b8cb679f7 100644
--- a/chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/enrollment_screen_handler.h
@@ -23,6 +23,16 @@ namespace chromeos {
 class ErrorScreensHistogramHelper;
 class HelpAppLauncher;
 
+// Possible error states of the Active Directory screen. Must be in the same
+// order as ACTIVE_DIRECTORY_ERROR_STATE enum values.
+enum class ActiveDirectoryErrorState {
+  NONE = 0,
+  MACHINE_NAME_INVALID = 1,
+  MACHINE_NAME_TOO_LONG = 2,
+  BAD_USERNAME = 3,
+  BAD_PASSWORD = 4,
+};
+
 // WebUIMessageHandler implementation which handles events occurring on the
 // page, such as the user pressing the signin button.
 class EnrollmentScreenHandler