transcoder: Mark benchmark frame rate iteration invariant

Mark the video frame rate counter as
kIsIterationInvariantRate so that correct value
is reported even when the benchmark
iterates.

Bug: 175889103
Test: ./MediaTranscoderBenchmark

Change-Id: If924d12c38f41f483bd9223ce9557568fec3de99
diff --git a/media/libmediatranscoding/transcoder/benchmark/MediaTranscoderBenchmark.cpp b/media/libmediatranscoding/transcoder/benchmark/MediaTranscoderBenchmark.cpp
index 602bde6..b270ed5 100644
--- a/media/libmediatranscoding/transcoder/benchmark/MediaTranscoderBenchmark.cpp
+++ b/media/libmediatranscoding/transcoder/benchmark/MediaTranscoderBenchmark.cpp
@@ -154,8 +154,8 @@
             if (strncmp(mime, "video/", 6) == 0) {
                 int32_t frameCount;
                 if (AMediaFormat_getInt32(srcFormat, AMEDIAFORMAT_KEY_FRAME_COUNT, &frameCount)) {
-                    state.counters[PARAM_VIDEO_FRAME_RATE] =
-                            benchmark::Counter(frameCount, benchmark::Counter::kIsRate);
+                    state.counters[PARAM_VIDEO_FRAME_RATE] = benchmark::Counter(
+                            frameCount, benchmark::Counter::kIsIterationInvariantRate);
                 }
             }