Add severity into RTC logging callbacks

Bug: webrtc:9945
Change-Id: I5022f63103503d2213492d3cd1a6953fe658fda7
Reviewed-on: https://webrtc-review.googlesource.com/c/108981
Commit-Queue: Jiawei Ou <ouj@fb.com>
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25510}

sdk/objc/api/logging/RTCCallbackLogger.h

@@ -15,6 +15,10 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+typedef void (^RTCCallbackLoggerMessageHandler)(NSString *message);
+typedef void (^RTCCallbackLoggerMessageAndSeverityHandler)(NSString *message,
+                                                           RTCLoggingSeverity severity);
+
 // This class intercepts WebRTC logs and forwards them to a registered block.
 // This class is not threadsafe.
 RTC_OBJC_EXPORT
@@ -23,10 +27,12 @@ RTC_OBJC_EXPORT
 // The severity level to capture. The default is kRTCLoggingSeverityInfo.
 @property(nonatomic, assign) RTCLoggingSeverity severity;
 
-// The callback will be called on the same thread that does the logging, so
-// if the logging callback can be slow it may be a good idea to implement
-// dispatching to some other queue.
-- (void)start:(nullable void (^)(NSString*))callback;
+// The callback handler will be called on the same thread that does the
+// logging, so if the logging callback can be slow it may be a good idea
+// to implement dispatching to some other queue.
+- (void)start:(nullable RTCCallbackLoggerMessageHandler)handler;
+- (void)startWithMessageAndSeverityHandler:
+        (nullable RTCCallbackLoggerMessageAndSeverityHandler)handler;
 
 - (void)stop;