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

Source/modules/mediasource/SourceBuffer.idl

Index: Source/modules/mediasource/SourceBuffer.idl
diff --git a/Source/modules/mediasource/SourceBuffer.idl b/Source/modules/mediasource/SourceBuffer.idl
index 5099e0d6c9c997328a94549b3458b7d0ddb99ea8..915e269fdb4d6c30b629dd6ef62a8a9b1940e0f0 100644
--- a/Source/modules/mediasource/SourceBuffer.idl
+++ b/Source/modules/mediasource/SourceBuffer.idl
@@ -42,6 +42,12 @@
     // 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);