Stopped using the NetEqDecoder enum internally in NetEq.

NetEqDecoder is still used in the external interfaces, but this change
opens up the ability to use SdpAudioFormats directly, once appropriate
interfaces have been added.

BUG=webrtc:5805

Review-Url: https://codereview.webrtc.org/2355503002
Cr-Commit-Position: refs/heads/master@{#14368}
diff --git a/webrtc/modules/audio_coding/neteq/timestamp_scaler.cc b/webrtc/modules/audio_coding/neteq/timestamp_scaler.cc
index fc3a846..b7eeb4b 100644
--- a/webrtc/modules/audio_coding/neteq/timestamp_scaler.cc
+++ b/webrtc/modules/audio_coding/neteq/timestamp_scaler.cc
@@ -45,12 +45,12 @@
   if (!(info->IsComfortNoise() || info->IsDtmf())) {
     // Do not change the timestamp scaling settings for DTMF or CNG.
     numerator_ = info->SampleRateHz();
-    if (info->codec_type == NetEqDecoder::kDecoderArbitrary) {
-      // We have no format mapping for "arbitrary" external codecs, so we cannot
-      // support timestamp scaling of them.
+    if (info->GetFormat().clockrate_hz == 0) {
+      // If the clockrate is invalid (i.e. with an old-style external codec)
+      // we cannot do any timestamp scaling.
       denominator_ = numerator_;
     } else {
-      denominator_ = info->GetFormat()->clockrate_hz;
+      denominator_ = info->GetFormat().clockrate_hz;
     }
   }
   if (numerator_ != denominator_) {