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/RTCSessionDescription.mm

@@ -0,0 +1,102 @@
+/*
+ *  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 "RTCSessionDescription+Private.h"
+
+#import "NSString+StdString.h"
+#import "WebRTC/RTCLogging.h"
+
+#include "webrtc/base/checks.h"
+
+@implementation RTCSessionDescription
+
+@synthesize type = _type;
+@synthesize sdp = _sdp;
+
++ (NSString *)stringForType:(RTCSdpType)type {
+  std::string string = [[self class] stdStringForType:type];
+  return [NSString stringForStdString:string];
+}
+
++ (RTCSdpType)typeForString:(NSString *)string {
+  std::string typeString = string.stdString;
+  return [[self class] typeForStdString:typeString];
+}
+
+- (instancetype)initWithType:(RTCSdpType)type sdp:(NSString *)sdp {
+  NSParameterAssert(sdp.length);
+  if (self = [super init]) {
+    _type = type;
+    _sdp = [sdp copy];
+  }
+  return self;
+}
+
+- (NSString *)description {
+  return [NSString stringWithFormat:@"RTCSessionDescription:\n%@\n%@",
+                                    [[self class] stringForType:_type],
+                                    _sdp];
+}
+
+#pragma mark - Private
+
+- (webrtc::SessionDescriptionInterface *)nativeDescription {
+  webrtc::SdpParseError error;
+
+  webrtc::SessionDescriptionInterface *description =
+      webrtc::CreateSessionDescription([[self class] stdStringForType:_type],
+                                       _sdp.stdString,
+                                       &error);
+
+  if (!description) {
+    RTCLogError(@"Failed to create session description: %s\nline: %s",
+                error.description.c_str(),
+                error.line.c_str());
+  }
+
+  return description;
+}
+
+- (instancetype)initWithNativeDescription:
+    (const webrtc::SessionDescriptionInterface *)nativeDescription {
+  NSParameterAssert(nativeDescription);
+  std::string sdp;
+  nativeDescription->ToString(&sdp);
+  RTCSdpType type = [[self class] typeForStdString:nativeDescription->type()];
+
+  return [self initWithType:type
+                        sdp:[NSString stringForStdString:sdp]];
+}
+
++ (std::string)stdStringForType:(RTCSdpType)type {
+  switch (type) {
+    case RTCSdpTypeOffer:
+      return webrtc::SessionDescriptionInterface::kOffer;
+    case RTCSdpTypePrAnswer:
+      return webrtc::SessionDescriptionInterface::kPrAnswer;
+    case RTCSdpTypeAnswer:
+      return webrtc::SessionDescriptionInterface::kAnswer;
+  }
+}
+
++ (RTCSdpType)typeForStdString:(const std::string &)string {
+  if (string == webrtc::SessionDescriptionInterface::kOffer) {
+    return RTCSdpTypeOffer;
+  } else if (string == webrtc::SessionDescriptionInterface::kPrAnswer) {
+    return RTCSdpTypePrAnswer;
+  } else if (string == webrtc::SessionDescriptionInterface::kAnswer) {
+    return RTCSdpTypeAnswer;
+  } else {
+    RTC_NOTREACHED();
+    return RTCSdpTypeOffer;
+  }
+}
+
+@end