Reland of Injectable Obj-C video codecs

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCVideoCodecH264.h

+/*
+ *  Copyright 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.
+ */
+
+#import <Foundation/Foundation.h>
+
+#import <WebRTC/RTCMacros.h>
+#import <WebRTC/RTCVideoCodecFactory.h>
+
+/** Class for H264 specific config. */
+typedef NS_ENUM(NSUInteger, RTCH264PacketizationMode) {
+  NonInterleaved = 0,  // Mode 1 - STAP-A, FU-A is allowed
+  SingleNalUnit        // Mode 0 - only single NALU allowed
+};
+
+RTC_EXPORT
+@interface RTCCodecSpecificInfoH264 : NSObject<RTCCodecSpecificInfo>
+
+@property(nonatomic, assign) RTCH264PacketizationMode packetizationMode;
+
+@end
+
+/** Encoder. */
+RTC_EXPORT
+@interface RTCVideoEncoderH264 : NSObject<RTCVideoEncoder>
+@end
+
+/** Decoder. */
+RTC_EXPORT
+@interface RTCVideoDecoderH264 : NSObject<RTCVideoDecoder>
+@end
+
+/** Encoder factory. */
+RTC_EXPORT
+@interface RTCVideoEncoderFactoryH264 : NSObject<RTCVideoEncoderFactory>
+@end
+
+/** Decoder factory. */
+RTC_EXPORT
+@interface RTCVideoDecoderFactoryH264 : NSObject<RTCVideoDecoderFactory>
+@end