Introduce CreateDataChannelOrError

Deprecate CreateDataChannel, and make it a simple wrapper function.

Bug: webrtc:12796
Change-Id: I053d75a264596ba87ca734a29df9241de93a80c3
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/219784
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34130}
diff --git a/examples/unityplugin/simple_peer_connection.cc b/examples/unityplugin/simple_peer_connection.cc
index 128ca76..c7e5185 100644
--- a/examples/unityplugin/simple_peer_connection.cc
+++ b/examples/unityplugin/simple_peer_connection.cc
@@ -497,8 +497,9 @@
   struct webrtc::DataChannelInit init;
   init.ordered = true;
   init.reliable = true;
-  data_channel_ = peer_connection_->CreateDataChannel("Hello", &init);
-  if (data_channel_.get()) {
+  auto result = peer_connection_->CreateDataChannelOrError("Hello", &init);
+  if (result.ok()) {
+    data_channel_ = result.MoveValue();
     data_channel_->RegisterObserver(this);
     RTC_LOG(LS_INFO) << "Succeeds to create data channel";
     return true;