An example of Unity native plugin of webrtc for Windows OS
Unity native plugin has to use Pinvoke technology in its APIs
This plugin dll can also be used by Windows C# applications other than
Unity.

BUG=webrtc:7389

Review-Url: https://codereview.webrtc.org/2823783002
Cr-Commit-Position: refs/heads/master@{#18108}
diff --git a/webrtc/examples/unityplugin/unity_plugin_apis.h b/webrtc/examples/unityplugin/unity_plugin_apis.h
new file mode 100644
index 0000000..bcd1af3
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+++ b/webrtc/examples/unityplugin/unity_plugin_apis.h
@@ -0,0 +1,83 @@
+/*
+ *  Copyright (c) 2017 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.
+ */
+
+// This file provides an example of unity native plugin APIs.
+
+#ifndef WEBRTC_EXAMPLES_UNITYPLUGIN_UNITY_PLUGIN_APIS_H_
+#define WEBRTC_EXAMPLES_UNITYPLUGIN_UNITY_PLUGIN_APIS_H_
+
+#include <stdint.h>
+
+// Defintions of callback functions.
+typedef void (*VIDEOFRAMEREADY_CALLBACK)(uint8_t* buffer,
+                                         uint32_t width,
+                                         uint32_t height,
+                                         uint32_t stride);
+typedef void (*LOCALDATACHANNELREADY_CALLBACK)();
+typedef void (*DATAFROMEDATECHANNELREADY_CALLBACK)(const char* msg);
+typedef void (*FAILURE_CALLBACK)(const char* msg);
+typedef void (*LOCALSDPREADYTOSEND_CALLBACK)(const char* msg);
+typedef void (*ICECANDIDATEREADYTOSEND_CALLBACK)(const char* msg);
+typedef void (*AUDIOBUSREADY_CALLBACK)(const void* audio_data,
+                                       int bits_per_sample,
+                                       int sample_rate,
+                                       int number_of_channels,
+                                       int number_of_frames);
+
+#define WEBRTC_PLUGIN_API __declspec(dllexport)
+extern "C" {
+// Create a peerconnection and return a unique peer connection id.
+WEBRTC_PLUGIN_API int CreatePeerConnection();
+// Close a peerconnection.
+WEBRTC_PLUGIN_API bool ClosePeerConnection(int peer_connection_id);
+// Add a audio stream. If audio_only is true, the stream only has an audio
+// track and no video track.
+WEBRTC_PLUGIN_API bool AddStream(int peer_connection_id, bool audio_only);
+// Add a data channel to peer connection.
+WEBRTC_PLUGIN_API bool AddDataChannel(int peer_connection_id);
+// Create a peer connection offer.
+WEBRTC_PLUGIN_API bool CreateOffer(int peer_connection_id);
+// Create a peer connection answer.
+WEBRTC_PLUGIN_API bool CreateAnswer(int peer_connection_id);
+// Send data through data channel.
+WEBRTC_PLUGIN_API bool SendDataViaDataChannel(int peer_connection_id,
+                                              const char* data);
+// Set audio control. If is_mute=true, no audio will playout. If is_record=true,
+// AUDIOBUSREADY_CALLBACK will be called every 10 ms.
+WEBRTC_PLUGIN_API bool SetAudioControl(int peer_connection_id,
+                                       bool is_mute,
+                                       bool is_record);
+
+// Register callback functions.
+WEBRTC_PLUGIN_API bool RegisterOnVideoFramReady(
+    int peer_connection_id,
+    VIDEOFRAMEREADY_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnLocalDataChannelReady(
+    int peer_connection_id,
+    LOCALDATACHANNELREADY_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnDataFromDataChannelReady(
+    int peer_connection_id,
+    DATAFROMEDATECHANNELREADY_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnFailure(int peer_connection_id,
+                                         FAILURE_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnAudioBusReady(int peer_connection_id,
+                                               AUDIOBUSREADY_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnLocalSdpReadytoSend(
+    int peer_connection_id,
+    LOCALSDPREADYTOSEND_CALLBACK callback);
+WEBRTC_PLUGIN_API bool RegisterOnIceCandiateReadytoSend(
+    int peer_connection_id,
+    ICECANDIDATEREADYTOSEND_CALLBACK callback);
+WEBRTC_PLUGIN_API int ReceivedSdp(int peer_connection_id, const char* sdp);
+WEBRTC_PLUGIN_API bool ReceivedIceCandidate(int peer_connection_id,
+                                            const char* ice_candidate);
+}
+
+#endif  // WEBRTC_EXAMPLES_UNITYPLUGIN_UNITY_PLUGIN_APIS_H_