Enable round-tripping and updating of SourceBuffer timestamp offset

public/platform/WebSourceBuffer.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 28 matching lines @@
 public:
     enum AppendMode {
         AppendModeSegments,
         AppendModeSequence
     };
 
     virtual ~WebSourceBuffer() { }
     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.

[jamesr, 2014/02/27 01:18:27]

can you just land the chromium implementation first to avoid this extra step?

it's not clear to me if the return value will remain bool after the transition

[wolenetz, 2014/02/27 01:44:56]

I was going on acolwell@'s separate suggestion to keep the chromium and blink
changes independent. The end result of landing these two will be the chromium
implementation will override the bool append() here, letting me then land
another two independent changes that get rid of the old void append in each of
Blink and Chromium.

Keeping these first two independently land-able improves chances of more rapidly
getting the later two changes landed, too.

+    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;
 
     // Set presentation timestamp for the start of append window.
     virtual void setAppendWindowStart(double) = 0;
 
     // Set presentation timestamp for the end of append window.
     virtual void setAppendWindowEnd(double) = 0;
 
     virtual void removedFromMediaSource() = 0;
 };
 
 } // namespace blink
 
 #endif