Add Blink side support for SourceBuffer.appendWindowStart & SourceBuffer.appendWindowEnd.

Source/modules/mediasource/SourceBuffer.idl

 /*
  * 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 24 matching lines @@
 ] interface SourceBuffer : EventTarget {
 
     readonly attribute boolean updating;
 
     // Returns the time ranges buffered.
     [GetterRaisesException] readonly attribute TimeRanges buffered;
 
     // Applies an offset to media segment timestamps.
     [SetterRaisesException] attribute double timestampOffset;
 
+    // Presentation timestamp for the start of append window.
+    [SetterRaisesException] attribute double appendWindowStart;
+
+    // Presentation timestamp for the end of append window.
+    [SetterRaisesException] attribute double appendWindowEnd;
+
     // Append segment data.
     [RaisesException] void appendBuffer(ArrayBuffer data);
     [RaisesException] void appendBuffer(ArrayBufferView data);
 
     // Abort the current segment append sequence.
     [RaisesException] void abort();
     [RaisesException] void remove(double start, double end);
 };