Add AbslStringify for RtcErrorType and RtcErrorDetail

Drive-by: fix MakeVal in rtc_base/checks.h to ensure that StrCat is
used for types that have AbslStringify.

Bug: None
Change-Id: Ia78c65da18b4a826365a6a2c741f11809640197f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/374345
Reviewed-by: Evan Shrubsole <eshr@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43779}

api/rtc_error.h

@@ -105,6 +105,16 @@ enum class RTCErrorDetailType {
 RTC_EXPORT absl::string_view ToString(RTCErrorType error);
 RTC_EXPORT absl::string_view ToString(RTCErrorDetailType error);
 
+template <typename Sink>
+void AbslStringify(Sink& sink, RTCErrorType error) {
+  sink.Append(ToString(error));
+}
+
+template <typename Sink>
+void AbslStringify(Sink& sink, RTCErrorDetailType error_detail) {
+  sink.Append(ToString(error_detail));
+}
+
 // Roughly corresponds to RTCError in the web api. Holds an error type, a
 // message, and possibly additional information specific to that error.
 //

rtc_base/checks.h

@@ -212,6 +212,7 @@ inline Val<CheckArgType::kVoidP, const void*> MakeVal(
 // The enum class types are not implicitly convertible to arithmetic types.
 template <typename T,
           absl::enable_if_t<std::is_enum<T>::value &&
+                            !absl::HasAbslStringify<T>::value &&
                             !std::is_arithmetic<T>::value>* = nullptr>
 inline decltype(MakeVal(std::declval<absl::underlying_type_t<T>>())) MakeVal(
     T x) {