Simplify reference count juggling

src/core/lib/security/credentials/google_default/compute_engine_channel_credentials.cc

@@ -61,10 +61,8 @@ grpc_channel_credentials* grpc_compute_engine_channel_credentials_create(
   grpc_alts_credentials_options_destroy(options);
 
   auto creds = new grpc_google_default_channel_credentials(
-      alts_creds != nullptr ? alts_creds->Ref() : nullptr,
+      grpc_core::RefCountedPtr<grpc_channel_credentials>(alts_creds),
-      ssl_creds != nullptr ? ssl_creds->Ref() : nullptr);
+      grpc_core::RefCountedPtr<grpc_channel_credentials>(ssl_creds));
-  if (ssl_creds) ssl_creds->Unref();
-  if (alts_creds) alts_creds->Unref();
 
   return creds;
 }

src/core/lib/security/credentials/google_default/google_default_credentials.cc

@@ -333,10 +333,8 @@ end:
     grpc_alts_credentials_options_destroy(options);
     auto creds =
         grpc_core::MakeRefCounted<grpc_google_default_channel_credentials>(
-            alts_creds != nullptr ? alts_creds->Ref() : nullptr,
+						grpc_core::RefCountedPtr<grpc_channel_credentials>(alts_creds),
-            ssl_creds != nullptr ? ssl_creds->Ref() : nullptr);
+						grpc_core::RefCountedPtr<grpc_channel_credentials>(ssl_creds));
-    if (ssl_creds) ssl_creds->Unref();
-    if (alts_creds) alts_creds->Unref();
     result = grpc_composite_channel_credentials_create(
         creds.get(), call_creds.get(), nullptr);
     GPR_ASSERT(result != nullptr);