Name change from stream label to stream id for spec compliance.

Bug: webrtc:7932
Change-Id: I66f33597342394083256f050cac2a00a68042302
Reviewed-on: https://webrtc-review.googlesource.com/59280
Commit-Queue: Seth Hampson <shampson@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Reviewed-by: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22276}

pc/peerconnectionfactory.h

@@ -1,3 +1,4 @@
+
 /*
  *  Copyright 2011 The WebRTC project authors. All Rights Reserved.
  *
@@ -57,8 +58,8 @@ class PeerConnectionFactory : public PeerConnectionFactoryInterface {
 
   bool Initialize();
 
-  rtc::scoped_refptr<MediaStreamInterface>
-      CreateLocalMediaStream(const std::string& label) override;
+  rtc::scoped_refptr<MediaStreamInterface> CreateLocalMediaStream(
+      const std::string& stream_id) override;
 
   rtc::scoped_refptr<AudioSourceInterface> CreateAudioSource(
       const cricket::AudioOptions& options) override;