c2_e2e_test: Print drop frame rate instead of the count.

Originally when measuring the drop frame, we decode the video in loop.
The test didn't reply the count of total decoded frames.
This CL changes to print the drop frame rate instead of the count.

Bug: 155944233
Test: Run tast.arc.VideoDecodeAccelPerf.h264_2160p_30fps

Change-Id: I62aee92184d6fbb35b5dc737fcf85eaeeba28ac1
(cherry picked from commit 7373fd74f8786288db1586ba9e32ed83cea293cf)

tests/c2_e2e_test/jni/mediacodec_decoder.cpp

@@ -457,4 +457,10 @@ int64_t MediaCodecDecoder::GetReleaseTimestampNs(size_t frame_order) {
     return base_timestamp_ns_ + frame_order * kSecToNs / frame_rate_;
 }
 
+double MediaCodecDecoder::dropped_frame_rate() const {
+    assert(received_outputs_ > 0);
+
+    return (double)drop_frame_count_ / (double)received_outputs_;
+}
+
 }  // namespace android

tests/c2_e2e_test/jni/mediacodec_decoder.h

@@ -64,7 +64,7 @@ public:
 
     void StopLooping() { looping_ = false; }
 
-    int32_t dropped_frame_count() const { return drop_frame_count_; }
+    double dropped_frame_rate() const;
 
     void OnAsyncInputAvailable(int32_t idx);
     void OnAsyncOutputAvailable(int32_t idx, AMediaCodecBufferInfo* info);

tests/c2_e2e_test/jni/video_decoder_e2e_test.cpp

@@ -356,7 +356,7 @@ void C2VideoDecoderE2ETest::TestFPSBody() {
     double fps = fps_calculator.CalculateFPS();
     printf("[LOG] Measured decoder FPS: %.4f\n", fps);
     EXPECT_GE(fps, static_cast<double>(g_env->min_fps_no_render()));
-    printf("[LOG] Dropped frames: %d\n", decoder_->dropped_frame_count());
+    printf("[LOG] Dropped frames rate: %lf\n", decoder_->dropped_frame_rate());
 }
 
 TEST_F(C2VideoDecoderSurfaceE2ETest, TestFPS) {