Add interface to signal a network down event.

- In real-time mode encoding will be paused until the network is back up.
- In buffering mode the encoder will keep encoding, and packets will be
  buffered at the sender. When the buffer grows above the target delay
  encoding will be paused.
- Fixes a couple of issues related to pacing which was found with the new test.
- Introduces different max bitrates for pacing and for encoding. This allows
  the pacer to faster get rid of the queue after a network down event.

(Work based on issue 1237004)

BUG=1524
TESTS=trybots,vie_auto_test

Review URL: https://webrtc-codereview.appspot.com/1258004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3730 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/main/source/media_optimization.cc

@@ -94,6 +94,12 @@ VCMMediaOptimization::SetTargetRates(WebRtc_UWord32 target_bitrate,
                                      WebRtc_UWord8 &fractionLost,
                                      WebRtc_UWord32 roundTripTimeMs)
 {
+    // TODO(holmer): Consider putting this threshold only on the video bitrate,
+    // and not on protection.
+    if (_maxBitRate > 0 &&
+        target_bitrate > static_cast<uint32_t>(_maxBitRate)) {
+      target_bitrate = _maxBitRate;
+    }
     VCMProtectionMethod *selectedMethod = _lossProtLogic->SelectedMethod();
     float target_bitrate_kbps = static_cast<float>(target_bitrate) / 1000.0f;
     _lossProtLogic->UpdateBitRate(target_bitrate_kbps);