Add histogram stats for number of cpu/quality adapt changes per minute for sent video streams:

webrtc/video_send_stream.h

Index: webrtc/video_send_stream.h
diff --git a/webrtc/video_send_stream.h b/webrtc/video_send_stream.h
index 8a82a6df4d81a447f708f9d5c56673a61e2e123b..f6083940508c0756f861f8e2a5237704d4d77308 100644
--- a/webrtc/video_send_stream.h
+++ b/webrtc/video_send_stream.h
@@ -70,8 +70,9 @@ class VideoSendStream {
     bool bw_limited_resolution = false;
     bool cpu_limited_resolution = false;
     // Total number of times resolution as been requested to be changed due to
-    // CPU adaptation.
+    // CPU/quality adaptation.
     int number_of_cpu_adapt_changes = 0;
+    int number_of_quality_adapt_changes = 0;
     std::map<uint32_t, StreamStats> substreams;
   };