Update the BWE when the network route changes.

webrtc/modules/congestion_controller/congestion_controller_unittest.cc

Index: webrtc/modules/congestion_controller/congestion_controller_unittest.cc
diff --git a/webrtc/modules/congestion_controller/congestion_controller_unittest.cc b/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
index c82c75daf3cdd5f6f794cb26a5f715947d02ba3d..8edfe498ec5b34e1210a3bbf0c7497e58cefbdba 100644
--- a/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
+++ b/webrtc/modules/congestion_controller/congestion_controller_unittest.cc
@@ -124,6 +124,20 @@ TEST_F(CongestionControllerTest, SignalNetworkState) {
   controller_->SignalNetworkState(kNetworkDown);
 }
 
+TEST_F(CongestionControllerTest, ResetBweBitrates) {
+  int new_bitrate = 200000;
+  EXPECT_CALL(observer_, OnNetworkChanged(new_bitrate, _, _));
+  EXPECT_CALL(*pacer_, SetEstimatedBitrate(new_bitrate));
+  controller_->ResetBweBitrates(new_bitrate, -1, -1);
+
+  // If the bitrate is reset to -1, the new starting bitrate will be
+  // the minimum default bitrate 10000bps.
+  int min_default_bitrate = 10000;
+  EXPECT_CALL(observer_, OnNetworkChanged(min_default_bitrate, _, _));
+  EXPECT_CALL(*pacer_, SetEstimatedBitrate(min_default_bitrate));
+  controller_->ResetBweBitrates(-1, -1, -1);

[stefan-webrtc, 2016/05/30 06:47:03]

Is this a good behavior? Shouldn't we instead let it reset to the previous
bitrate? So essentially this call would be a no-op except for recreating BWE
objects.

[honghaiz3, 2016/05/31 16:58:03]

What do you mean by "previous bitrate"?
If you mean the bitrate right before we make the call, it then would be a no-op.

If you mean the bitrate before the last round of BWE, then we need to remember
the history. 
Plus the concept of "last round of BWE" is not clear to me.

What I attempt to do is to mimic the behavior of SetBweBitrates(-1, -1, -1) but
after creating a set
of BWE objects. So it would be the same as the state when the system starts with
SetBweBitrates(-1, -1, -1). 
WDYT? 

[stefan-webrtc, 2016/05/31 17:27:49]

I see.

I was thinking that if we want to reset only the max and min, then it would be
good to be able to pass in -1 as start bitrate. But I guess that is what it
already does, I may have just misunderstood.

+}
+
 TEST_F(CongestionControllerTest,
        SignalNetworkStateAndQueueIsFullAndEstimateChange) {
   // Send queue is full