Fix crash when all acks in a feedback message arrive too late.

webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc

Index: webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
diff --git a/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc b/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
index 44407b37e95ef2d68668879636ab481821216c3c..b72d00604f3f00103c4d24e24605e86804c65ae5 100644
--- a/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
+++ b/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
@@ -25,6 +25,20 @@ const PacedPacketInfo kPacingInfo0(0, kNumProbesCluster0, 2000);
 const PacedPacketInfo kPacingInfo1(1, kNumProbesCluster1, 4000);
 }  // namespace
 
+TEST_F(DelayBasedBweTest, NoCrashEmptyFeedback) {
+  std::vector<PacketFeedback> packet_feedback_vector;
+  bitrate_estimator_->IncomingPacketFeedbackVector(packet_feedback_vector);
+}
+
+TEST_F(DelayBasedBweTest, NoCrashOnlyLostFeedback) {
+  std::vector<PacketFeedback> packet_feedback_vector;
+  packet_feedback_vector.push_back(
+      PacketFeedback(-1, -1, 0, 1500, PacedPacketInfo()));
+  packet_feedback_vector.push_back(
+      PacketFeedback(-1, -1, 1, 1500, PacedPacketInfo()));
+  bitrate_estimator_->IncomingPacketFeedbackVector(packet_feedback_vector);
+}
+
 TEST_F(DelayBasedBweTest, ProbeDetection) {
   int64_t now_ms = clock_.TimeInMilliseconds();
   uint16_t seq_num = 0;