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

public/web/WebSourceBuffer.h

Index: public/web/WebSourceBuffer.h
diff --git a/public/web/WebSourceBuffer.h b/public/web/WebSourceBuffer.h
index 064626cda9b94ff4f61c35b10b2bb8d73f8af9d9..6dd88917bf383f69204de7d9b8f16d756e59c540 100644
--- a/public/web/WebSourceBuffer.h
+++ b/public/web/WebSourceBuffer.h
@@ -43,6 +43,8 @@ public:
     virtual void append(const unsigned char* data, unsigned length) = 0;
     virtual void abort() = 0;
     virtual bool setTimestampOffset(double) = 0;
+    virtual void setAppendWindowStart(double) = 0;
+    virtual void setAppendWindowEnd(double) = 0;
     virtual void removedFromMediaSource() = 0;
 };