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..0f026c856a963b00db43a1ee2ab0642e3e24005e 100644
--- a/public/platform/WebSourceBuffer.h
+++ b/public/platform/WebSourceBuffer.h
@@ -46,6 +46,18 @@ public:
     virtual bool setMode(AppendMode) = 0;
     virtual WebTimeRanges buffered() = 0;
     virtual void append(const unsigned char* data, unsigned length) = 0;
+
+    // If the append does not update the source buffer's timestamp offset,
+    // returns false and |*newTimestampOffset| is unchanged.
+    // Otherwise, returns true and |*newTimestampOffset| contains the updated offset.
+    // FIXME: Remove both the void append(...) and this method's default implementation once
+    // the Chromium implementation of this signature has landed. See http://crbug.com/249422.
+    virtual bool append(const unsigned char* data, unsigned length, double* newTimestampOffset)
+    {
+        append(data, length);
+        return false;
+    }
+
     virtual void abort() = 0;
     virtual void remove(double start, double end) = 0;
     virtual bool setTimestampOffset(double) = 0;