addIceCandidate with callback into Android's SDK.

Bug: webrtc:12609
Change-Id: I059a246f5ade201b6a8decac264a8dd79fef3f9a
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212740
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Xavier Lepaul‎ <xalep@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33681}

sdk/android/api/org/webrtc/AddIceObserver.java

@@ -0,0 +1,20 @@
+/*
+ *  Copyright 2021 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+package org.webrtc;
+
+/** Interface to handle completion of addIceCandidate  */
+public interface AddIceObserver {
+  /** Called when ICE candidate added successfully.*/
+  @CalledByNative public void onAddSuccess();
+
+  /** Called when ICE candidate addition failed.*/
+  @CalledByNative public void onAddFailure(String error);
+}