Fix QuicConnectionHelper's alarm implementation

net/quic/quic_connection_helper_test.cc

Index: net/quic/quic_connection_helper_test.cc
diff --git a/net/quic/quic_connection_helper_test.cc b/net/quic/quic_connection_helper_test.cc
index e228d12cf49c34aa003ccf1dc8ebd24cc8df0489..4f248cc30a17a8030e855c0fa58796f41811db2a 100644
--- a/net/quic/quic_connection_helper_test.cc
+++ b/net/quic/quic_connection_helper_test.cc
@@ -38,6 +38,7 @@ class TestDelegate : public QuicAlarm::Delegate {
   }
 
   bool fired() const { return fired_; }
+  void Clear() { fired_= false; }
 
  private:
   bool fired_;
@@ -307,6 +308,35 @@ TEST_F(QuicConnectionHelperTest, CreateAlarmAndReset) {
   EXPECT_TRUE(delegate->fired());
 }
 
+TEST_F(QuicConnectionHelperTest, CreateAlarmAndResetEarlier) {
+  TestDelegate* delegate = new TestDelegate();
+  scoped_ptr<QuicAlarm> alarm(helper_->CreateAlarm(delegate));
+
+  QuicTime::Delta delta = QuicTime::Delta::FromMicroseconds(3);
+  alarm->Set(clock_.Now().Add(delta));
+  alarm->Cancel();
+  QuicTime::Delta new_delta = QuicTime::Delta::FromMicroseconds(1);
+  alarm->Set(clock_.Now().Add(new_delta));
+
+  // Both alarm tasks will be posted.
+  ASSERT_EQ(3u, runner_->GetPostedTasks().size());
+
+  // The earlier task will execute and will fire the alarm.
+  runner_->RunNextTask();
+  EXPECT_EQ(QuicTime::Zero().Add(new_delta), clock_.Now());
+  EXPECT_TRUE(delegate->fired());
+  delegate->Clear();
+
+  // The latter task is still posted.
+  ASSERT_EQ(2u, runner_->GetPostedTasks().size());
+
+  // When the latter task is executed, the weak ptr will be invalid and
+  // the alarm will not fire.
+  runner_->RunNextTask();
+  EXPECT_EQ(QuicTime::Zero().Add(delta), clock_.Now());
+  EXPECT_FALSE(delegate->fired());
+}
+
 TEST_F(QuicConnectionHelperTest, TestRTORetransmission) {
   AddWrite(SYNCHRONOUS, ConstructDataPacket(1));
   AddWrite(SYNCHRONOUS, ConstructDataPacket(2));