Adopt absl::string_view in system_wrappers/

Bug: webrtc:13579
Change-Id: Id0e6515c63a3c9aa6d7effef7a2bd8b5ef35af09
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262245
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Ali Tofigh <alito@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36904}

sdk/objc/api/peerconnection/RTCMetrics.mm

@@ -12,12 +12,14 @@
 
 #import "RTCMetricsSampleInfo+Private.h"
 
+#include "rtc_base/string_utils.h"
+
 void RTCEnableMetrics(void) {
   webrtc::metrics::Enable();
 }
 
 NSArray<RTC_OBJC_TYPE(RTCMetricsSampleInfo) *> *RTCGetAndResetMetrics(void) {
-  std::map<std::string, std::unique_ptr<webrtc::metrics::SampleInfo>>
+  std::map<std::string, std::unique_ptr<webrtc::metrics::SampleInfo>, rtc::AbslStringViewCmp>
       histograms;
   webrtc::metrics::GetAndReset(&histograms);