Propagating total_bitrate_bps from BitrateAllocator to ProbeController, part 3.

Trigger on total bitrate change.

Bug: webrtc:8955
Change-Id: I2373a1b7f139c7ea748a9641593e714d6895c8f6
Reviewed-on: https://webrtc-review.googlesource.com/59323
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22323}

modules/congestion_controller/goog_cc/probe_controller.h

@@ -37,6 +37,11 @@ class ProbeController {
                    int64_t max_bitrate_bps,
                    int64_t at_time_ms);
 
+  // The total bitrate, as opposed to the max bitrate, is the sum of the
+  // configured bitrates for all active streams.
+  void OnMaxTotalAllocatedBitrate(int64_t max_total_allocated_bitrate,
+                                  int64_t at_time_ms);
+
   void OnNetworkAvailability(NetworkAvailability msg);
 
   void SetEstimatedBitrate(int64_t bitrate_bps, int64_t at_time_ms);