Enable round-tripping and updating of SourceBuffer timestamp offset

Source/modules/mediasource/WebKitSourceBuffer.cpp

Index: Source/modules/mediasource/WebKitSourceBuffer.cpp
diff --git a/Source/modules/mediasource/WebKitSourceBuffer.cpp b/Source/modules/mediasource/WebKitSourceBuffer.cpp
index f460311fb3dc0bea48d95d62227b62850ebe8afb..f10a46b0f19a9c9ae5739e0c7fa666ee69162f9c 100644
--- a/Source/modules/mediasource/WebKitSourceBuffer.cpp
+++ b/Source/modules/mediasource/WebKitSourceBuffer.cpp
@@ -136,7 +136,10 @@ void WebKitSourceBuffer::append(PassRefPtr<Uint8Array> data, ExceptionState& exc
     m_source->openIfInEndedState();
 
     // Steps 6 & beyond are handled by m_webSourceBuffer.
-    m_webSourceBuffer->append(data->data(), data->length());
+
+    // Use null for |timestampOffset| parameter because the prefixed API does not allow appends
+    // to update timestampOffset.
+    m_webSourceBuffer->append(data->data(), data->length(), 0);
 }
 
 void WebKitSourceBuffer::abort(ExceptionState& exceptionState)