Add support for logging absl::string_view.

Bug: webrtc:8982
Change-Id: I5691f91ea663756666cf187ee223ede50f87d5f0
Reviewed-on: https://webrtc-review.googlesource.com/99840
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24707}

rtc_base/logging.cc

@@ -540,6 +540,9 @@ void Log(const LogArgType* fmt, ...) {
       case LogArgType::kStdString:
         log_message.stream() << *va_arg(args, const std::string*);
         break;
+      case LogArgType::kStringView:
+        log_message.stream() << *va_arg(args, const absl::string_view*);
+        break;
       case LogArgType::kVoidP:
         log_message.stream() << rtc::ToHex(
             reinterpret_cast<uintptr_t>(va_arg(args, const void*)));