Changes name of RtpTransceiverInit's stream_labels to stream_ids.

The naming convention according to the spec is stream id, not stream
labels.Changing things now to be spec compliant, before it is widely
used. This also includes changes to objective C wrapper code to be in
sync with the change.

Bug: webrtc:7932
Change-Id: I5705e6d8a647aaeed860316466a7320132f24b00
Reviewed-on: https://webrtc-review.googlesource.com/59301
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Commit-Queue: Seth Hampson <shampson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22316}
diff --git a/sdk/objc/Framework/Headers/WebRTC/RTCRtpTransceiver.h b/sdk/objc/Framework/Headers/WebRTC/RTCRtpTransceiver.h
index a670e2b..db0fd1c 100644
--- a/sdk/objc/Framework/Headers/WebRTC/RTCRtpTransceiver.h
+++ b/sdk/objc/Framework/Headers/WebRTC/RTCRtpTransceiver.h
@@ -34,7 +34,7 @@
 @property(nonatomic) RTCRtpTransceiverDirection direction;
 
 /** The added RTCRtpTransceiver will be added to these streams. */
-@property(nonatomic) NSArray<NSString *> *streamLabels;
+@property(nonatomic) NSArray<NSString *> *streamIds;
 
 /** TODO(bugs.webrtc.org/7600): Not implemented. */
 @property(nonatomic) NSArray<RTCRtpEncodingParameters *> *sendEncodings;