Revert of Split iOS sdk in to separate targets (patchset #1 id:1 of https://codereview.webrtc.org/2890733003/ )

Reason for revert:
Still problems with downstream projects

Original issue's description:
> Reland of Split iOS sdk in to separate targets (patchset #1 id:1 of https://codereview.webrtc.org/2890513002/ )
>
> Reason for revert:
> Fixing downstream breakages
>
> Original issue's description:
> > Revert of Split iOS sdk in to separate targets (patchset #13 id:280001 of https://codereview.webrtc.org/2862543002/ )
> >
> > Reason for revert:
> > Breaking downstream projects.
> >
> > Original issue's description:
> > > Split iOS sdk in to separate targets
> > >
> > > This CL splits the iOS sdk into separate static libraries for video,
> > > audio, ui, common, and peerconnection-related code. This will in the
> > > future make it easier to compile WebRTC without unneeded components.
> > >
> > > BUG=webrtc:4867
> > >
> > > Review-Url: https://codereview.webrtc.org/2862543002
> > > Cr-Commit-Position: refs/heads/master@{#18166}
> > > Committed: 52c83fe710
> >
> > TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,kthelgason@webrtc.org
> > # Skipping CQ checks because original CL landed less than 1 days ago.
> > NOPRESUBMIT=true
> > NOTREECHECKS=true
> > NOTRY=true
> > BUG=webrtc:4867
> >
> > Review-Url: https://codereview.webrtc.org/2890513002
> > Cr-Commit-Position: refs/heads/master@{#18170}
> > Committed: 9756238084
>
> TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,charujain@webrtc.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:4867
>
> Review-Url: https://codereview.webrtc.org/2890733003
> Cr-Commit-Position: refs/heads/master@{#18174}
> Committed: d51e042492

TBR=magjed@webrtc.org,denicija@webrtc.org,tkchin@webrtc.org,henrika@webrtc.org,charujain@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:4867

Review-Url: https://codereview.webrtc.org/2893593002
Cr-Commit-Position: refs/heads/master@{#18182}

webrtc/sdk/objc/Framework/Classes/RTCDataChannel+Private.h

@@ -0,0 +1,49 @@
+/*
+ *  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 "WebRTC/RTCDataChannel.h"
+
+#include "webrtc/api/datachannelinterface.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RTCDataBuffer ()
+
+/**
+ * The native DataBuffer representation of this RTCDatabuffer object. This is
+ * needed to pass to the underlying C++ APIs.
+ */
+@property(nonatomic, readonly) const webrtc::DataBuffer *nativeDataBuffer;
+
+/** Initialize an RTCDataBuffer from a native DataBuffer. */
+- (instancetype)initWithNativeBuffer:(const webrtc::DataBuffer&)nativeBuffer;
+
+@end
+
+
+@interface RTCDataChannel ()
+
+/** Initialize an RTCDataChannel from a native DataChannelInterface. */
+- (instancetype)initWithNativeDataChannel:
+    (rtc::scoped_refptr<webrtc::DataChannelInterface>)nativeDataChannel
+    NS_DESIGNATED_INITIALIZER;
+
++ (webrtc::DataChannelInterface::DataState)
+    nativeDataChannelStateForState:(RTCDataChannelState)state;
+
++ (RTCDataChannelState)dataChannelStateForNativeState:
+    (webrtc::DataChannelInterface::DataState)nativeState;
+
++ (NSString *)stringForState:(RTCDataChannelState)state;
+
+@end
+
+NS_ASSUME_NONNULL_END