Add field trial to update quality scaler QP thresholds for Android HW encoder.

webrtc/modules/video_coding/utility/quality_scaler.cc

Index: webrtc/modules/video_coding/utility/quality_scaler.cc
diff --git a/webrtc/modules/video_coding/utility/quality_scaler.cc b/webrtc/modules/video_coding/utility/quality_scaler.cc
index 3dd3dde93a92b0a7f84357a20e1e6b6db95a3d8e..a5cb90e0515386ad6de4260249c2c423013bc884 100644
--- a/webrtc/modules/video_coding/utility/quality_scaler.cc
+++ b/webrtc/modules/video_coding/utility/quality_scaler.cc
@@ -112,6 +112,8 @@ QualityScaler::QualityScaler(AdaptationObserverInterface* observer,
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
   RTC_DCHECK(observer_ != nullptr);
   check_qp_task_ = new CheckQPTask(this);
+  LOG(LS_INFO) << "QP thresholds: low: " << thresholds_.low
+               << ", high: " << thresholds_.high;
 }
 
 QualityScaler::~QualityScaler() {
@@ -144,6 +146,8 @@ void QualityScaler::CheckQP() {
   // Check if we should scale down due to high frame drop.
   const rtc::Optional<int> drop_rate = framedrop_percent_.GetAverage();
   if (drop_rate && *drop_rate >= kFramedropPercentThreshold) {
+    LOG(LS_INFO) << "Drop rate " << *drop_rate
+                 << " has been high , asking for lower resolution.";

[kthelgason, 2017/03/22 07:38:58]

There is a bug here (https://bugs.chromium.org/p/webrtc/issues/detail?id=7373)
about reducing the amount of logging done by the quality scaler. Some have
thought it's confusing that it will log even though resolution is at max/min.
Feel free to weigh in on the bug if you feel these log lines are useful.

[AlexG, 2017/03/22 19:53:45]

I am not sure regarding the proper logging here. Probably worth to address in a
separate CL

[stefan-webrtc, 2017/03/23 17:58:04]

I think the current logging is confusing, so I'd probably leave it out if you
don't think it's really necessary. I It will periodically log this (and below)
throughout the call if it can't get a higher/lower resolution

[AlexG, 2017/03/23 19:25:08]

Done. I removed "asking for lower/higher resolution logs". May still worth to
keep QP log to monitor average QP?

     ReportQPHigh();
     return;
   }
@@ -151,11 +155,15 @@ void QualityScaler::CheckQP() {
   // Check if we should scale up or down based on QP.
   const rtc::Optional<int> avg_qp = average_qp_.GetAverage();
   if (avg_qp && *avg_qp > thresholds_.high) {
+    LOG(LS_INFO) << "QP " << *avg_qp
+                 << " has been high , asking for lower resolution.";
     ReportQPHigh();
     return;
   }
   if (avg_qp && *avg_qp <= thresholds_.low) {
     // QP has been low. We want to try a higher resolution.
+    LOG(LS_INFO) << "QP " << *avg_qp
+                 << " has been low, asking for higher resolution.";
     ReportQPLow();
     return;
   }
@@ -163,14 +171,12 @@ void QualityScaler::CheckQP() {
 
 void QualityScaler::ReportQPLow() {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
-  LOG(LS_INFO) << "QP has been low, asking for higher resolution.";
   ClearSamples();
   observer_->AdaptUp(AdaptationObserverInterface::AdaptReason::kQuality);
 }
 
 void QualityScaler::ReportQPHigh() {
   RTC_DCHECK_CALLED_SEQUENTIALLY(&task_checker_);
-  LOG(LS_INFO) << "QP has been high , asking for lower resolution.";
   ClearSamples();
   observer_->AdaptDown(AdaptationObserverInterface::AdaptReason::kQuality);
   // If we've scaled down, wait longer before scaling up again.