Adopt absl::string_view in rtc_base/log_sinks

This is part of a large scale effort to increase adoption of
absl::string_view across the WebRTC code base.

This CL adds absl::string_view versions of the OnLogMessage functions in
rtc::LogSink. The const std::string& versions are kept for now since
downstream clients use subclasses of LogSink and need to be migrated
before these are removed.

Bug: webrtc:13579
Change-Id: I57bb72ad503805ff0ca16f1d7aece2d44c65cb73
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/253980
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Owners-Override: Xavier Lepaul‎ <xalep@webrtc.org>
Commit-Queue: Ali Tofigh <alito@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36189}
diff --git a/rtc_base/logging_unittest.cc b/rtc_base/logging_unittest.cc
index dc1208f..cd8d753 100644
--- a/rtc_base/logging_unittest.cc
+++ b/rtc_base/logging_unittest.cc
@@ -16,6 +16,7 @@
 
 #include <algorithm>
 
+#include "absl/strings/string_view.h"
 #include "rtc_base/arraysize.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/event.h"
@@ -34,7 +35,10 @@
 
  private:
   void OnLogMessage(const std::string& message) override {
-    log_data_->append(message);
+    OnLogMessage(absl::string_view(message));
+  }
+  void OnLogMessage(absl::string_view message) override {
+    log_data_->append(message.begin(), message.end());
   }
   std::string* const log_data_;
 };