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/api/peer_connection_interface.h b/api/peer_connection_interface.h
index 75c4d3c..e815f19 100644
--- a/api/peer_connection_interface.h
+++ b/api/peer_connection_interface.h
@@ -920,9 +920,24 @@
   // Also, calling CreateDataChannel is the only way to get a data "m=" section
   // in SDP, so it should be done before CreateOffer is called, if the
   // application plans to use data channels.
+  virtual RTCErrorOr<rtc::scoped_refptr<DataChannelInterface>>
+  CreateDataChannelOrError(const std::string& label,
+                           const DataChannelInit* config) {
+    return RTCError(RTCErrorType::INTERNAL_ERROR, "dummy function called");
+  }
+  // TODO(crbug.com/788659): Remove "virtual" below and default implementation
+  // above once mock in Chrome is fixed.
+  ABSL_DEPRECATED("Use CreateDataChannelOrError")
   virtual rtc::scoped_refptr<DataChannelInterface> CreateDataChannel(
       const std::string& label,
-      const DataChannelInit* config) = 0;
+      const DataChannelInit* config) {
+    auto result = CreateDataChannelOrError(label, config);
+    if (!result.ok()) {
+      return nullptr;
+    } else {
+      return result.MoveValue();
+    }
+  }
 
   // NOTE: For the following 6 methods, it's only safe to dereference the
   // SessionDescriptionInterface on signaling_thread() (for example, calling