Update/move RTCVideoRendererAdapter to webrtc/api/objc.

BUG=
R=tkchin@webrtc.org

Review URL: https://codereview.webrtc.org/1533323003 .

Patch from Jon Hjelle <hjon@andyet.net>.

Cr-Commit-Position: refs/heads/master@{#11347}
diff --git a/webrtc/api/objc/RTCVideoRendererAdapter+Private.h b/webrtc/api/objc/RTCVideoRendererAdapter+Private.h
new file mode 100644
index 0000000..807eea4
--- /dev/null
+++ b/webrtc/api/objc/RTCVideoRendererAdapter+Private.h
@@ -0,0 +1,42 @@
+/*
+ *  Copyright 2015 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.
+ */
+
+#import "RTCVideoRendererAdapter.h"
+
+#include "talk/app/webrtc/mediastreaminterface.h"
+
+#import "RTCVideoRenderer.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCVideoRendererAdapter ()
+
+/**
+ * The Objective-C video renderer passed to this adapter during construction.
+ * Calls made to the webrtc::VideoRenderInterface will be adapted and passed to
+ * this video renderer.
+ */
+@property(nonatomic, readonly) id<RTCVideoRenderer> videoRenderer;
+
+/**
+ * The native VideoRendererInterface surface exposed by this adapter. Calls made
+ * to this interface will be adapted and passed to the RTCVideoRenderer supplied
+ * during construction. This pointer is unsafe and owned by this class.
+ */
+@property(nonatomic, readonly)
+    webrtc::VideoRendererInterface *nativeVideoRenderer;
+
+/** Initialize an RTCVideoRendererAdapter with an RTCVideoRenderer. */
+- (instancetype)initWithNativeRenderer:(id<RTCVideoRenderer>)videoRenderer
+    NS_DESIGNATED_INITIALIZER;
+
+@end
+
+NS_ASSUME_NONNULL_END