Enable round-tripping and updating of SourceBuffer timestamp offset

public/platform/WebSourceBuffer.h

Index: public/platform/WebSourceBuffer.h
diff --git a/public/platform/WebSourceBuffer.h b/public/platform/WebSourceBuffer.h
index e789648be8f95d62073d2a76d7bdaf74fbe6a0c4..1f34a0c52ab9696ab3baf3b5f732cda54e8c0139 100644
--- a/public/platform/WebSourceBuffer.h
+++ b/public/platform/WebSourceBuffer.h
@@ -45,7 +45,11 @@ public:
     virtual ~WebSourceBuffer() { }
     virtual bool setMode(AppendMode) = 0;
     virtual WebTimeRanges buffered() = 0;
-    virtual void append(const unsigned char* data, unsigned length) = 0;
+
+    // Appends data and runs the segment parser loop algorithm.
+    // The algorithm may update |*timestampOffset| if |timestampOffset| is not null.
+    virtual void append(const unsigned char* data, unsigned length, double* timestampOffset) = 0;
+
     virtual void abort() = 0;
     virtual void remove(double start, double end) = 0;
     virtual bool setTimestampOffset(double) = 0;