Fix problems with absolute value function.

net/quic/congestion_control/tcp_cubic_sender.cc

Index: net/quic/congestion_control/tcp_cubic_sender.cc
diff --git a/net/quic/congestion_control/tcp_cubic_sender.cc b/net/quic/congestion_control/tcp_cubic_sender.cc
index 742129bef37c00c47843dad1b2155e067a73b910..25183ef39f961417e5ba7f56b472bbe931f52afa 100644
--- a/net/quic/congestion_control/tcp_cubic_sender.cc
+++ b/net/quic/congestion_control/tcp_cubic_sender.cc
@@ -340,7 +340,8 @@ void TcpCubicSender::UpdateRtt(QuicTime::Delta rtt) {
   } else {
     mean_deviation_ = QuicTime::Delta::FromMicroseconds(
         kOneMinusBeta * mean_deviation_.ToMicroseconds() +
-        kBeta * abs(smoothed_rtt_.ToMicroseconds() - rtt.ToMicroseconds()));
+        kBeta *
+            std::abs(smoothed_rtt_.ToMicroseconds() - rtt.ToMicroseconds()));
     smoothed_rtt_ = QuicTime::Delta::FromMicroseconds(
         kOneMinusAlpha * smoothed_rtt_.ToMicroseconds() +
         kAlpha * rtt.ToMicroseconds());