Implement RtpParameters.transaction_id for PC RtpSenderInterface

The transaction_id field should be refreshed for every getParameters()
call and checked at each setParameters() call.
This also checks that getParameters() was ever called to return a proper
error code.

Bug: webrtc:7580
Change-Id: I6c6fe289542e486fc422cdc61577982b0529d4c1
Reviewed-on: https://webrtc-review.googlesource.com/70820
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23120}

sdk/objc/Framework/Classes/PeerConnection/RTCRtpParameters.mm

@@ -10,11 +10,13 @@
 
 #import "RTCRtpParameters+Private.h"
 
+#import "NSString+StdString.h"
 #import "RTCRtpCodecParameters+Private.h"
 #import "RTCRtpEncodingParameters+Private.h"
 
 @implementation RTCRtpParameters
 
+@synthesize transactionId = _transactionId;
 @synthesize encodings = _encodings;
 @synthesize codecs = _codecs;
 
@@ -25,6 +27,7 @@
 - (instancetype)initWithNativeParameters:
     (const webrtc::RtpParameters &)nativeParameters {
   if (self = [self init]) {
+    _transactionId = [NSString stringForStdString:nativeParameters.transaction_id];
     NSMutableArray *encodings = [[NSMutableArray alloc] init];
     for (const auto &encoding : nativeParameters.encodings) {
       [encodings addObject:[[RTCRtpEncodingParameters alloc]
@@ -43,7 +46,8 @@
 }
 
 - (webrtc::RtpParameters)nativeParameters {
-    webrtc::RtpParameters parameters;
+  webrtc::RtpParameters parameters;
+  parameters.transaction_id = [NSString stdStringForString:_transactionId];
   for (RTCRtpEncodingParameters *encoding in _encodings) {
     parameters.encodings.push_back(encoding.nativeParameters);
   }