Consolidate and improve audio decoding test for all decoders.

media/filters/opus_audio_decoder.cc

Index: media/filters/opus_audio_decoder.cc
diff --git a/media/filters/opus_audio_decoder.cc b/media/filters/opus_audio_decoder.cc
index b7d93c0ef2b5ccc067c07551da865567054c8889..bf59adf691e671c27535f6dd8c70407e016dec88 100644
--- a/media/filters/opus_audio_decoder.cc
+++ b/media/filters/opus_audio_decoder.cc
@@ -292,15 +292,16 @@ void OpusAudioDecoder::Stop() {
   CloseDecoder();
 }
 
-OpusAudioDecoder::~OpusAudioDecoder() {}
+OpusAudioDecoder::~OpusAudioDecoder() {
+  DCHECK(!opus_decoder_);
+}
 
 void OpusAudioDecoder::DecodeBuffer(
     const scoped_refptr<DecoderBuffer>& input,
     const DecodeCB& decode_cb) {
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK(!decode_cb.is_null());
-
-  DCHECK(input.get());
+  DCHECK(input);
 
   // Libopus does not buffer output. Decoding is complete when an end of stream
   // input buffer is received.