Make protection_overhead_rate configurable through field trial.

Bug: None
Change-Id: I0a4e03d5f8134809c44d2d0ff88c4b4c8b8a9eaa
Reviewed-on: https://webrtc-review.googlesource.com/c/107341
Commit-Queue: Ying Wang <yinwa@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25293}
diff --git a/modules/video_coding/fec_controller_default.h b/modules/video_coding/fec_controller_default.h
index a95eced..9d79a61 100644
--- a/modules/video_coding/fec_controller_default.h
+++ b/modules/video_coding/fec_controller_default.h
@@ -42,6 +42,7 @@
   void UpdateWithEncodedData(const size_t encoded_image_length,
                              const FrameType encoded_image_frametype) override;
   bool UseLossVectorMask() override;
+  float GetProtectionOverheadRateThreshold();
 
  private:
   enum { kBitrateAverageWinMs = 1000 };
@@ -52,6 +53,7 @@
       RTC_GUARDED_BY(crit_sect_);
   size_t max_payload_size_ RTC_GUARDED_BY(crit_sect_);
   RTC_DISALLOW_COPY_AND_ASSIGN(FecControllerDefault);
+  const float overhead_threshold_;
 };
 
 }  // namespace webrtc