[chromecast] Fix build with enable_mojo_media=true.

chromecast/media/cma/pipeline/media_pipeline_impl.cc

Index: chromecast/media/cma/pipeline/media_pipeline_impl.cc
diff --git a/chromecast/media/cma/pipeline/media_pipeline_impl.cc b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
index d3e78cb58a518a995b554adff3c42d8a0fbd2f14..4cf1e342776d697ae14ae022485ca95f8f56e15a 100644
--- a/chromecast/media/cma/pipeline/media_pipeline_impl.cc
+++ b/chromecast/media/cma/pipeline/media_pipeline_impl.cc
@@ -143,8 +143,6 @@ void MediaPipelineImpl::SetClient(const MediaPipelineClient& client) {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(!client.error_cb.is_null());
   DCHECK(!client.buffering_state_cb.is_null());
-  DCHECK(!client.pipeline_backend_created_cb.is_null());
-  DCHECK(!client.pipeline_backend_destroyed_cb.is_null());
   client_ = client;
 }