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..58e4221063c13cbe1d69b086768631f2c74325fc 100644
--- a/public/platform/WebSourceBuffer.h
+++ b/public/platform/WebSourceBuffer.h
@@ -33,6 +33,8 @@
 
 #include "WebTimeRange.h"
 
+#include <limits>

[wolenetz, 2014/02/25 22:49:34]

There's a lint error for the sequencing of header includes. I copied this
sequence from another example in Blink. Should <limits> be before or after
"WebTimeRange.h" here?

+
 namespace blink {
 
 class WebSourceBuffer {
@@ -50,6 +52,16 @@ public:
     virtual void remove(double start, double end) = 0;
     virtual bool setTimestampOffset(double) = 0;
 
+    // Retrieve the implementation's updated timestamp offset, if any. If the
+    // implementation has not updated the offset since its construction or the
+    // last setTimestampOffset(), returns NaN instead of the actual timestamp
+    // offset. This allows caller to exactly round-trip a user-specified offset
+    // and implementation to update the offset.
+    virtual double updatedTimestampOffset()
+    {
+        return std::numeric_limits<double>::quiet_NaN();
+    }
+
     // Set presentation timestamp for the start of append window.
     virtual void setAppendWindowStart(double) = 0;