[Video] Add dummy video/audio tracks inactive to select them later.

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 99dd8a4216d0dc46a8bd81bc17c869ad0195e874..84f3930e8006570fbc734ac9a1c1207f1094f9ae 100644
--- a/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
+++ b/third_party/WebKit/Source/modules/mediasource/SourceBuffer.cpp
@@ -101,6 +101,11 @@ WTF::String webTimeRangesToString(const WebTimeRanges& ranges) {
   return stringBuilder.toString();
 }
 
+bool hasAudioVideoTracks() {
+  return RuntimeEnabledFeatures::audioVideoTracksEnabled() ||
+         RuntimeEnabledFeatures::backgroundVideoTrackOptimizationEnabled();
+}
+
 }  // namespace
 
 SourceBuffer* SourceBuffer::create(
@@ -269,12 +274,12 @@ void SourceBuffer::setTimestampOffset(double offset,
 }
 
 AudioTrackList& SourceBuffer::audioTracks() {
-  DCHECK(RuntimeEnabledFeatures::audioVideoTracksEnabled());
+  DCHECK(hasAudioVideoTracks());
   return *m_audioTracks;
 }
 
 VideoTrackList& SourceBuffer::videoTracks() {
-  DCHECK(RuntimeEnabledFeatures::audioVideoTracksEnabled());
+  DCHECK(hasAudioVideoTracks());
   return *m_videoTracks;
 }
 
@@ -569,7 +574,7 @@ void SourceBuffer::removedFromMediaSource() {
     abortIfUpdating();
   }
 
-  if (RuntimeEnabledFeatures::audioVideoTracksEnabled()) {
+  if (hasAudioVideoTracks()) {
     DCHECK(m_source);
     if (m_source->mediaElement()->audioTracks().length() > 0 ||
         m_source->mediaElement()->videoTracks().length() > 0) {
@@ -592,7 +597,7 @@ double SourceBuffer::highestPresentationTimestamp() {
 }
 
 void SourceBuffer::removeMediaTracks() {
-  DCHECK(RuntimeEnabledFeatures::audioVideoTracksEnabled());
+  DCHECK(hasAudioVideoTracks());
   // Spec:
   // http://w3c.github.io/media-source/#widl-MediaSource-removeSourceBuffer-void-SourceBuffer-sourceBuffer
   DCHECK(m_source);
@@ -756,7 +761,7 @@ bool SourceBuffer::initializationSegmentReceived(
   DCHECK(m_source->mediaElement());
   DCHECK(m_updating);
 
-  if (!RuntimeEnabledFeatures::audioVideoTracksEnabled()) {
+  if (!hasAudioVideoTracks()) {
     if (!m_firstInitializationSegmentReceived) {
       m_source->setSourceBufferActive(this, true);
       m_firstInitializationSegmentReceived = true;