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

net/quic/quic_alarm.cc

Index: net/quic/quic_alarm.cc
diff --git a/net/quic/quic_alarm.cc b/net/quic/quic_alarm.cc
index e1d4a16ae9c1d2a99dc929bac84884777a767a85..b5aca8caa175aae288f0d6f7c23f39b61bfed29a 100644
--- a/net/quic/quic_alarm.cc
+++ b/net/quic/quic_alarm.cc
@@ -27,6 +27,19 @@ void QuicAlarm::Cancel() {
   CancelImpl();
 }
 
+void QuicAlarm::Update(QuicTime deadline, QuicTime::Delta granularity) {
+  if (!deadline.IsInitialized()) {

[wtc, 2014/08/15 19:03:54]

Just curious: why do we need this behavior when we already provide a public
Cancel() method?

[ramant (doing other things), 2014/08/15 19:18:33]

Ian: would appreciate your reasoning (is it a convenient method?)

[Ian Swett, 2014/08/15 20:11:54]

It is convenient, and semantically more accurate, but most importantly it allows
the granularity optimization of not canceling and setting an alarm when the time
changes a small amount.  This can save a lot of CPU, as mentioned.

+    Cancel();
+    return;
+  }
+  if (std::abs(deadline.Subtract(deadline_).ToMicroseconds()) <
+          granularity.ToMicroseconds()) {
+    return;
+  }
+  Cancel();
+  Set(deadline);
+}
+
 bool QuicAlarm::IsSet() const {
   return deadline_.IsInitialized();
 }