Make UBSan warnings fatal and fix the existing ones

webrtc/modules/pacing/alr_detector.cc

Index: webrtc/modules/pacing/alr_detector.cc
diff --git a/webrtc/modules/pacing/alr_detector.cc b/webrtc/modules/pacing/alr_detector.cc
index 7d62b212511c56be3c0a779445fdeb1fa434bd8c..68732105c1db20c8380df4cc10032439212d2542 100644
--- a/webrtc/modules/pacing/alr_detector.cc
+++ b/webrtc/modules/pacing/alr_detector.cc
@@ -67,8 +67,9 @@ void AlrDetector::OnBytesSent(size_t bytes_sent, int64_t delta_time_ms) {
 
 void AlrDetector::SetEstimatedBitrate(int bitrate_bps) {
   RTC_DCHECK(bitrate_bps);
-  alr_budget_.set_target_rate_kbps(bitrate_bps * bandwidth_usage_percent_ /
-                                   (1000 * 100));
+  const auto target_rate_kbps = int64_t{bitrate_bps} *
+                                bandwidth_usage_percent_ / (1000 * 100);
+  alr_budget_.set_target_rate_kbps(rtc::dchecked_cast<int>(target_rate_kbps));
 }
 
 rtc::Optional<int64_t> AlrDetector::GetApplicationLimitedRegionStartTime()