[Chromecast] Update mixer unittests

BUG= internal b/71559266

Change-Id: I2750dd2e4b8eb012c7035ebb144aab6613538550
Reviewed-on: https://chromium-review.googlesource.com/937805Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539878}

chromecast/media/cma/backend/BUILD.gn

@@ -175,11 +175,11 @@ cast_source_set("for_mixer_audio") {
 test("cast_audio_backend_unittests") {
   testonly = true
   sources = [
+    "audio_fader_unittest.cc",
     "filter_group_unittest.cc",
     "mock_mixer_source.cc",
     "mock_mixer_source.h",
-
-    # "stream_mixer_unittest.cc",
+    "stream_mixer_unittest.cc",
   ]
 
   deps = [

chromecast/media/cma/backend/audio_fader.cc

@@ -84,7 +84,8 @@ void AudioFader::CompleteFill(::media::AudioBus* buffer, int filled_frames) {
     case State::kFadingOut:
       // Fade back in.
       state_ = State::kFadingIn;
-      fade_frames_remaining_ = fade_frames_ - fade_frames_remaining_;
+      fade_frames_remaining_ =
+          std::max(0, fade_frames_ - fade_frames_remaining_ - 1);
       break;
   }
   FadeIn(buffer, filled_frames);
@@ -100,7 +101,8 @@ void AudioFader::IncompleteFill(::media::AudioBus* buffer, int filled_frames) {
     case State::kFadingIn:
       // Fade back out.
       state_ = State::kFadingOut;
-      fade_frames_remaining_ = fade_frames_ - fade_frames_remaining_;
+      fade_frames_remaining_ =
+          std::max(0, fade_frames_ - fade_frames_remaining_ - 1);
       break;
     case State::kPlaying:
       // Fade out.