Change WebMediaPlayer::trackId to be the same as byteStreamTrackId

content/renderer/media/webmediaplayer_ms_unittest.cc

Index: content/renderer/media/webmediaplayer_ms_unittest.cc
diff --git a/content/renderer/media/webmediaplayer_ms_unittest.cc b/content/renderer/media/webmediaplayer_ms_unittest.cc
index 70520aac26b9e613a9fd83c008a960b89bad6388..584e0be350dfc7a0736e6073d5eb94d6ef9514c4 100644
--- a/content/renderer/media/webmediaplayer_ms_unittest.cc
+++ b/content/renderer/media/webmediaplayer_ms_unittest.cc
@@ -391,7 +391,7 @@ class WebMediaPlayerMSTest
                                                const blink::WebString& label,
                                                const blink::WebString& language,
                                                bool enabled) override {
-    return 0;
+    return blink::WebString();
   }
   void removeAudioTrack(blink::WebMediaPlayer::TrackId) override {}
   blink::WebMediaPlayer::TrackId addVideoTrack(const blink::WebString& id,
@@ -399,7 +399,7 @@ class WebMediaPlayerMSTest
                                                const blink::WebString& label,
                                                const blink::WebString& language,
                                                bool selected) override {
-    return 0;
+    return blink::WebString();
   }
   void removeVideoTrack(blink::WebMediaPlayer::TrackId) override {}
   void addTextTrack(blink::WebInbandTextTrack*) override {}