Pass time constanct to bwe smoothing filter.

BUG=webrtc:6443, webrtc:6303

Review-Url: https://codereview.webrtc.org/2518923003
Cr-Commit-Position: refs/heads/master@{#15266}
diff --git a/webrtc/modules/congestion_controller/include/congestion_controller.h b/webrtc/modules/congestion_controller/include/congestion_controller.h
index 8663489..1eb5b34 100644
--- a/webrtc/modules/congestion_controller/include/congestion_controller.h
+++ b/webrtc/modules/congestion_controller/include/congestion_controller.h
@@ -48,7 +48,8 @@
    public:
     virtual void OnNetworkChanged(uint32_t bitrate_bps,
                                   uint8_t fraction_loss,  // 0 - 255.
-                                  int64_t rtt_ms) = 0;
+                                  int64_t rtt_ms,
+                                  int64_t probing_interval_ms) = 0;
 
    protected:
     virtual ~Observer() {}