Generate and assign media track ids in demuxers.

third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp

Index: third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
diff --git a/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp b/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
index ea97613aa50607a193833f1304a868f28a7b82ad..ad9715aaa5548cb1952076f79fe03f16d848720b 100644
--- a/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
+++ b/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
@@ -590,8 +590,10 @@ WebVector<WebMediaPlayer::TrackId> SourceBuffer::initializationSegmentReceived(c
     unsigned resultIdx = 0;
     for (const auto& trackInfo : newTracks) {
         if (!RuntimeEnabledFeatures::audioVideoTracksEnabled()) {
-            static WebMediaPlayer::TrackId nextTrackId = 0;
-            result[resultIdx++] = ++nextTrackId;
+            static unsigned nextTrackId = 0;
+            StringBuilder stringBuilder;
+            stringBuilder.appendNumber(++nextTrackId);
+            result[resultIdx++] = stringBuilder.toString();
             continue;
         }
 
@@ -630,8 +632,8 @@ WebVector<WebMediaPlayer::TrackId> SourceBuffer::initializationSegmentReceived(c
         const char* logActionStr = m_firstInitializationSegmentReceived ? "using existing" : "added";
         const char* logTrackTypeStr = (trackInfo.trackType == WebMediaPlayer::AudioTrack) ? "audio" : "video";
         DVLOG(SOURCE_BUFFER_LOG_LEVEL) << __FUNCTION__ << "(" << this << ") " << logActionStr << " "
-            << logTrackTypeStr << " Track " << trackBase << "trackId=" << trackBase->trackId() << " id="
-            << trackBase->id() << " label=" << trackBase->label() << " lang=" << trackBase->language();
+            << logTrackTypeStr << " Track " << trackBase << " trackId=" << (String)trackBase->trackId()
+            << " label=" << trackBase->label() << " lang=" << trackBase->language();
 #endif
     }