Add probing to recover faster from large bitrate drops.

webrtc/modules/congestion_controller/probe_controller_unittest.cc

Index: webrtc/modules/congestion_controller/probe_controller_unittest.cc
diff --git a/webrtc/modules/congestion_controller/probe_controller_unittest.cc b/webrtc/modules/congestion_controller/probe_controller_unittest.cc
index 9fc0f5508849869ad2b2ad57ea0fbc3eb2f262a4..fc90b61badfaaf8746ec47d27eec2d9a8f923a0b 100644
--- a/webrtc/modules/congestion_controller/probe_controller_unittest.cc
+++ b/webrtc/modules/congestion_controller/probe_controller_unittest.cc
@@ -34,6 +34,8 @@ constexpr int kExponentialProbingTimeoutMs = 5000;
 
 constexpr int kAlrProbeInterval = 5000;
 
+constexpr int kAlrEndedTimeoutMs = 3000;
+
 }  // namespace
 
 class ProbeControllerTest : public ::testing::Test {
@@ -120,22 +122,48 @@ TEST_F(ProbeControllerTest, TestExponentialProbingTimeout) {
   probe_controller_->SetEstimatedBitrate(1800);
 }
 
-TEST_F(ProbeControllerTest, ProbeAfterEstimateDropInAlr) {
+TEST_F(ProbeControllerTest, RequestProbeInAlr) {
   EXPECT_CALL(pacer_, CreateProbeCluster(_)).Times(2);
   probe_controller_->SetBitrates(kMinBitrateBps, kStartBitrateBps,
                                  kMaxBitrateBps);
-  probe_controller_->SetEstimatedBitrate(500);
   testing::Mock::VerifyAndClearExpectations(&pacer_);
-
-  // When bandwidth estimate drops the controller should send a probe at the
-  // previous bitrate.
   EXPECT_CALL(pacer_, CreateProbeCluster(500)).Times(1);
   EXPECT_CALL(pacer_, GetApplicationLimitedRegionStartTime())
       .WillRepeatedly(
           Return(rtc::Optional<int64_t>(clock_.TimeInMilliseconds())));
   clock_.AdvanceTimeMilliseconds(kAlrProbeInterval + 1);
   probe_controller_->Process();
-  probe_controller_->SetEstimatedBitrate(50);
+  probe_controller_->RequestProbe(500);
+}
+
+TEST_F(ProbeControllerTest, RequestProbeWhenAlrEndedRecently) {
+  EXPECT_CALL(pacer_, CreateProbeCluster(_)).Times(2);
+  probe_controller_->SetBitrates(kMinBitrateBps, kStartBitrateBps,
+                                 kMaxBitrateBps);
+  testing::Mock::VerifyAndClearExpectations(&pacer_);
+  EXPECT_CALL(pacer_, CreateProbeCluster(500)).Times(1);
+  EXPECT_CALL(pacer_, GetApplicationLimitedRegionStartTime())
+      .WillRepeatedly(Return(rtc::Optional<int64_t>()));
+  clock_.AdvanceTimeMilliseconds(kAlrProbeInterval + 1);
+  probe_controller_->Process();
+  probe_controller_->SetAlrEndedTimeMs(clock_.TimeInMilliseconds());
+  clock_.AdvanceTimeMilliseconds(kAlrEndedTimeoutMs - 1);
+  probe_controller_->RequestProbe(500);
+}
+
+TEST_F(ProbeControllerTest, RequestProbeWhenAlrNotEndedRecently) {
+  EXPECT_CALL(pacer_, CreateProbeCluster(_)).Times(2);
+  probe_controller_->SetBitrates(kMinBitrateBps, kStartBitrateBps,
+                                 kMaxBitrateBps);
+  testing::Mock::VerifyAndClearExpectations(&pacer_);
+  EXPECT_CALL(pacer_, CreateProbeCluster(_)).Times(0);
+  EXPECT_CALL(pacer_, GetApplicationLimitedRegionStartTime())
+      .WillRepeatedly(Return(rtc::Optional<int64_t>()));
+  clock_.AdvanceTimeMilliseconds(kAlrProbeInterval + 1);
+  probe_controller_->Process();
+  probe_controller_->SetAlrEndedTimeMs(clock_.TimeInMilliseconds());
+  clock_.AdvanceTimeMilliseconds(kAlrEndedTimeoutMs + 1);
+  probe_controller_->RequestProbe(500);
 }
 
 TEST_F(ProbeControllerTest, PeriodicProbing) {