Replace uses of raw uint32's with a type-checked RtpTimeTicks data type.

media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc

Index: media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc
diff --git a/media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc b/media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc
index 6ada1e493ccf64d3f5e395f54842a096f6af60d1..02628b91dc07a7da457726350f245b034294bb18 100644
--- a/media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc
+++ b/media/cast/net/rtcp/receiver_rtcp_event_subscriber.cc
@@ -70,8 +70,8 @@ void ReceiverRtcpEventSubscriber::OnReceivePacketEvent(
 }
 
 struct CompareByFirst {
-  bool operator()(const std::pair<RtpTimestamp, RtcpEvent>& a,
-                  const std::pair<RtpTimestamp, RtcpEvent>& b) {
+  bool operator()(const std::pair<RtpTimeTicks, RtcpEvent>& a,
+                  const std::pair<RtpTimeTicks, RtcpEvent>& b) {
     return a.first < b.first;
   }
 };