Integrate helper macros for calling histograms with different names (real-time vs screenshare and r…

webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc

Index: webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc
diff --git a/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc b/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc
index 001937a2176ec65aa646244a533bef2459c04e23..872579bac3df25481be4a9137a5f48ed82ba1331 100644
--- a/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc
+++ b/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.cc
@@ -155,8 +155,8 @@ void SendSideBandwidthEstimation::UpdateUmaStats(int64_t now_ms,
   for (size_t i = 0; i < kNumUmaRampupMetrics; ++i) {
     if (!rampup_uma_stats_updated_[i] &&
         bitrate_kbps >= kUmaRampupMetrics[i].bitrate_kbps) {
-      RTC_HISTOGRAM_COUNTS_SPARSE_100000(kUmaRampupMetrics[i].metric_name,
-                                         now_ms - first_report_time_ms_);
+      RTC_HISTOGRAMS_COUNTS_100000(i, kUmaRampupMetrics[i].metric_name,

[stefan-webrtc, 2016/02/03 10:35:42]

It's not clear to me why these are now put on different indices. What does that
mean? They already have different names?

[pbos-webrtc, 2016/02/03 10:43:41]

To implement this fast we can't do the lookup on name every time this is called,
so we can cache it but that requires a fixed name per invocation. This macro
expands to

switch(i)
  case 0:
  HISTOGRAM(name)
  break;
  case 1:
  HISTOGRAM(name)
  break;

Which permits us to have a single lookup per index instead of per call. 0 must
always be the same metric name across the process, same for 1. It's a bit ugly,
but it prevents us from having to look for the metric every time we modify those
specific stats.

+                                   now_ms - first_report_time_ms_);
       rampup_uma_stats_updated_[i] = true;
     }
   }