Analyze quality of dropped frames in VideoProcessor.

Calculate quality metrics for dropped frames by comparing original
frame against last decoded one.

This feature makes comparison of encoders which do/don't drop frames
more fair.

The feature is controlled by analyze_quality_of_dropped_frames flag
and is disabled by default.

Bug: none
Change-Id: Ifab8df92d0b76e743ff3193c05d7c8dbd14921c4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/190660
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Sebastian Jansson <srte@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32518}

api/test/videocodec_test_fixture.h

@@ -138,6 +138,9 @@ class VideoCodecTestFixture {
       bool save_encoded_ivf = false;
       bool save_decoded_y4m = false;
     } visualization_params;
+
+    // Enables quality analysis for dropped frames.
+    bool analyze_quality_of_dropped_frames = false;
   };
 
   virtual ~VideoCodecTestFixture() = default;

api/test/videocodec_test_stats.h

@@ -67,6 +67,7 @@ class VideoCodecTestStats {
     int qp = -1;
 
     // Quality.
+    bool quality_analysis_successful = false;
     float psnr_y = 0.0f;
     float psnr_u = 0.0f;
     float psnr_v = 0.0f;