Fix multiple sound effects race getting decoder

In cases where kAudioDecoderLimit is > 1, SFX
are getting held to the 1 decoder limit. One decoder
is really about video, as that is the platform
limitation. Multiple sources may attempt to play
sound effects at the same time as these are just
audio only sources.

Bug: b/139941019
Test: Local build, test race condition and SFX.
Change-Id: Ieb7ea18674e58e06dc050f7ff2756e14021ab40d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1792451
Commit-Queue: Brett Kilty <brettk@google.com>
Reviewed-by: Kenneth MacKay <kmackay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694833}

chromecast/media/cma/backend/media_pipeline_backend_manager.cc

@@ -35,12 +35,8 @@ namespace media {
 
 namespace {
 
-#if BUILDFLAG(IS_CAST_AUDIO_ONLY) || BUILDFLAG(ENABLE_ASSISTANT)
 constexpr int kAudioDecoderLimit = std::numeric_limits<int>::max();
-#else
-constexpr int kAudioDecoderLimit = 1;
-#endif
-
+constexpr int kVideoDecoderLimit = 1;
 constexpr base::TimeDelta kPowerSaveWaitTime = base::TimeDelta::FromSeconds(5);
 
 }  // namespace
@@ -113,7 +109,8 @@ void MediaPipelineBackendManager::BackendUseVideoDecoder(
 bool MediaPipelineBackendManager::IncrementDecoderCount(DecoderType type) {
   DCHECK(media_task_runner_->BelongsToCurrentThread());
   DCHECK(type < NUM_DECODER_TYPES);
-  const int limit = (type == AUDIO_DECODER) ? kAudioDecoderLimit : 1;
+  const int limit =
+      (type == VIDEO_DECODER) ? kVideoDecoderLimit : kAudioDecoderLimit;
   if (decoder_count_[type] >= limit) {
     LOG(WARNING) << "Decoder limit reached for type " << type;
     return false;