Set the start bitrate to the delay-based BWE.

webrtc/call/call.cc

Index: webrtc/call/call.cc
diff --git a/webrtc/call/call.cc b/webrtc/call/call.cc
index 48072d0a0b71790bf2802289cef4324abdaaabe1..2cca579ae672c028c48e947f4c477fc79ed0a7b5 100644
--- a/webrtc/call/call.cc
+++ b/webrtc/call/call.cc
@@ -307,7 +307,7 @@ Call::Call(const Call::Config& config)
   RTC_DCHECK(configuration_thread_checker_.CalledOnValidThread());
   RTC_DCHECK(config.event_log != nullptr);
   RTC_DCHECK_GE(config.bitrate_config.min_bitrate_bps, 0);
-  RTC_DCHECK_GE(config.bitrate_config.start_bitrate_bps,
+  RTC_DCHECK_GT(config.bitrate_config.start_bitrate_bps,

[terelius, 2017/01/24 16:05:52]

Why not DCHECK_GE? That seems more natural to me.

[stefan-webrtc, 2017/01/24 16:29:43]

It's just a bit unclear to me why you'd want to start with a bitrate of zero. I
could allow it, but seems like a risk for bugs where we'd potentially get stuck
if some encoder can't just produces nothing.

WDYT, should I change?

[terelius, 2017/01/25 16:41:27]

Ok, I see. Is there a reason for allowing min_bitrate_bps_ == 0 in that case?

[stefan-webrtc, 2017/01/27 09:27:05]

Good question. It will immediately get clamped here:
https://cs.chromium.org/chromium/src/third_party/webrtc/modules/congestion_co...

I don't want to change this rule in this CL as 0 is default in the call config.
Let's pick it up separately if we feel it's worth changing.

                 config.bitrate_config.min_bitrate_bps);
   if (config.bitrate_config.max_bitrate_bps != -1) {
     RTC_DCHECK_GE(config.bitrate_config.max_bitrate_bps,
@@ -816,6 +816,7 @@ void Call::SetBitrateConfig(
   if (bitrate_config.start_bitrate_bps > 0)
     config_.bitrate_config.start_bitrate_bps = bitrate_config.start_bitrate_bps;
   config_.bitrate_config.max_bitrate_bps = bitrate_config.max_bitrate_bps;
+  RTC_DCHECK_NE(bitrate_config.start_bitrate_bps, 0);
   congestion_controller_->SetBweBitrates(bitrate_config.min_bitrate_bps,
                                          bitrate_config.start_bitrate_bps,
                                          bitrate_config.max_bitrate_bps);
@@ -912,6 +913,7 @@ void Call::OnNetworkRouteChanged(const std::string& transport_name,
                  << " bps, start: " << config_.bitrate_config.start_bitrate_bps
                  << " bps,  max: " << config_.bitrate_config.start_bitrate_bps
                  << " bps.";
+    RTC_DCHECK_GT(config_.bitrate_config.start_bitrate_bps, 0);
     congestion_controller_->ResetBweAndBitrates(
         config_.bitrate_config.start_bitrate_bps,
         config_.bitrate_config.min_bitrate_bps,