Handle BW drop in ALR region and initiate probing

Original change by isheriff@chromium.org: http://crrev.com/2387463002#ps40001

BUG=webrtc:6332
TBR=philipel@webrtc.org, stefan@webrtc.org

Review URL: https://codereview.webrtc.org/2432633002 .

Patch from Irfan Sheriff <isheriff@chromium.org>.

Cr-Commit-Position: refs/heads/master@{#14673}
diff --git a/webrtc/modules/congestion_controller/probe_controller.h b/webrtc/modules/congestion_controller/probe_controller.h
index 4cf34c3..efcc2a1 100644
--- a/webrtc/modules/congestion_controller/probe_controller.h
+++ b/webrtc/modules/congestion_controller/probe_controller.h
@@ -53,6 +53,7 @@
   int64_t time_last_probing_initiated_ms_ GUARDED_BY(critsect_);
   int estimated_bitrate_bps_ GUARDED_BY(critsect_);
   int max_bitrate_bps_ GUARDED_BY(critsect_);
+  int64_t last_alr_probing_time_ GUARDED_BY(critsect_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(ProbeController);
 };