Make enum NotificationOption's underlying type bool.

It only has 2 possible enum values.

Change-Id: I93480bc18ae986337b8c8735b4e4342718a2be37
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/81772
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fpdfdoc/cpdf_formfield.h b/core/fpdfdoc/cpdf_formfield.h
index 188477a..945545f 100644
--- a/core/fpdfdoc/cpdf_formfield.h
+++ b/core/fpdfdoc/cpdf_formfield.h
@@ -24,7 +24,7 @@
 class CPDF_Object;
 class CPDF_String;
 
-enum class NotificationOption { kDoNotNotify = 0, kNotify };
+enum class NotificationOption : bool { kDoNotNotify = false, kNotify = true };
 
 enum class FormFieldType : uint8_t {
   kUnknown = 0,