Convert media constants to constexpr.

media/filters/decrypting_audio_decoder.cc

Index: media/filters/decrypting_audio_decoder.cc
diff --git a/media/filters/decrypting_audio_decoder.cc b/media/filters/decrypting_audio_decoder.cc
index bc2b89d61ad2c00bfb7b142353f2c63545bd7443..eaa84114c7b0d85afb811cd0f41afb71caf1d305 100644
--- a/media/filters/decrypting_audio_decoder.cc
+++ b/media/filters/decrypting_audio_decoder.cc
@@ -114,7 +114,7 @@ void DecryptingAudioDecoder::Decode(const scoped_refptr<DecoderBuffer>& buffer,
 
   // Initialize the |next_output_timestamp_| to be the timestamp of the first
   // non-EOS buffer.
-  if (timestamp_helper_->base_timestamp() == kNoTimestamp() &&
+  if (timestamp_helper_->base_timestamp() == kNoTimestamp &&
       !buffer->end_of_stream()) {
     timestamp_helper_->SetBaseTimestamp(buffer->timestamp());
   }
@@ -323,7 +323,7 @@ void DecryptingAudioDecoder::OnKeyAdded() {
 void DecryptingAudioDecoder::DoReset() {
   DCHECK(init_cb_.is_null());
   DCHECK(decode_cb_.is_null());
-  timestamp_helper_->SetBaseTimestamp(kNoTimestamp());
+  timestamp_helper_->SetBaseTimestamp(kNoTimestamp);
   state_ = kIdle;
   base::ResetAndReturn(&reset_cb_).Run();
 }