Add an Update method on QuicAlarm which contains a granularity. Also

net/quic/quic_connection_test.cc

Index: net/quic/quic_connection_test.cc
diff --git a/net/quic/quic_connection_test.cc b/net/quic/quic_connection_test.cc
index 13f97bf436c9a65226141596283009b101f8fe5b..f798b37fd2a27ccf523320795c68ad8bd72f5923 100644
--- a/net/quic/quic_connection_test.cc
+++ b/net/quic/quic_connection_test.cc
@@ -2639,7 +2639,10 @@ TEST_P(QuicConnectionTest, PingAfterSend) {
   EXPECT_CALL(*send_algorithm_, OnCongestionEvent(true, _, _, _));
   ProcessAckPacket(&frame);
   EXPECT_TRUE(connection_.GetPingAlarm()->IsSet());
-  EXPECT_EQ(clock_.ApproximateNow().Add(QuicTime::Delta::FromSeconds(15)),
+  // The ping timer is set slightly less than 15 seconds in the future, because
+  // of the 1s ping timer alarm granularity.
+  EXPECT_EQ(clock_.ApproximateNow().Add(QuicTime::Delta::FromSeconds(15))
+                .Subtract(QuicTime::Delta::FromMilliseconds(5)),
             connection_.GetPingAlarm()->deadline());
 
   writer_->Reset();