VP9 decoder: replace DCHECK with error message

Bug: chromium:1016160
Change-Id: I0ef0db2b254829e7c0dff24b7a8da3a4056547ac
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157890
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29567}
diff --git a/modules/video_coding/codecs/vp9/vp9_impl.cc b/modules/video_coding/codecs/vp9/vp9_impl.cc
index 74d8e89..b926fe3 100644
--- a/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -1746,7 +1746,8 @@
           img->stride[VPX_PLANE_V] / 2, rtc::KeepRefUntilDone(img_buffer));
       break;
     default:
-      RTC_NOTREACHED();
+      RTC_LOG(LS_ERROR) << "Unsupported bit depth produced by the decoder: "
+                        << img->bit_depth;
       return WEBRTC_VIDEO_CODEC_NO_OUTPUT;
   }