Enable round-tripping and updating of WebSourceBufferImpl timestamp offset

content/renderer/media/websourcebuffer_impl.cc

Index: content/renderer/media/websourcebuffer_impl.cc
diff --git a/content/renderer/media/websourcebuffer_impl.cc b/content/renderer/media/websourcebuffer_impl.cc
index a7d8d8a537803b4f9a2a8bdf42777af21720a5a0..b8993134a51caa23d419bed6c5a467f59f6dc4e7 100644
--- a/content/renderer/media/websourcebuffer_impl.cc
+++ b/content/renderer/media/websourcebuffer_impl.cc
@@ -5,6 +5,7 @@
 #include "content/renderer/media/websourcebuffer_impl.h"
 
 #include "base/float_util.h"
+#include "media/base/buffers.h"
 #include "media/filters/chunk_demuxer.h"
 
 namespace content {
@@ -77,6 +78,15 @@ bool WebSourceBufferImpl::setTimestampOffset(double offset) {
   return demuxer_->SetTimestampOffset(id_, time_offset);
 }
 
+double WebSourceBufferImpl::updatedTimestampOffset() {
+  base::TimeDelta updated_offset = demuxer_->GetUpdatedTimestampOffset(id_);
+
+  if (updated_offset == media::kNoTimestamp())
+    return std::numeric_limits<double>::quiet_NaN();
+
+  return updated_offset.InSecondsF();
+}
+
 void WebSourceBufferImpl::setAppendWindowStart(double start) {
   demuxer_->SetAppendWindowStart(id_, DoubleToTimeDelta(start));
 }