mkvmuxer: Overload WriteEbmlHeader for backward compatibility

WriteEbmlHeader function was updated on
a321704b4c. It is a public function that
is exposed outside of the library. Overload it with an old signature
to maintain compatibility. The overloaded function writes the
doc_type_version as 2 by default (thereby retaining the old behavior).

Change-Id: If887a1bfa3e81e7e639c986a922aa5155faab2cf

mkvmuxer.cpp

@@ -95,6 +95,10 @@ bool WriteEbmlHeader(IMkvWriter* writer, uint64 doc_type_version) {
   return true;
 }
 
+bool WriteEbmlHeader(IMkvWriter* writer) {
+  return WriteEbmlHeader(writer, mkvmuxer::Segment::kDefaultDocTypeVersion);
+}
+
 bool ChunkedCopy(mkvparser::IMkvReader* source, mkvmuxer::IMkvWriter* dst,
                  mkvmuxer::int64 start, int64 size) {
   // TODO(vigneshv): Check if this is a reasonable value.

mkvmuxer.hpp

@@ -57,6 +57,10 @@ class IMkvWriter {
 
 // Writes out the EBML header for a WebM file. This function must be called
 // before any other libwebm writing functions are called.
+bool WriteEbmlHeader(IMkvWriter* writer, uint64 doc_type_version);
+
+// Deprecated. Writes out EBML header with doc_type_version as
+// kDefaultDocTypeVersion. Exists for backward compatibility.
 bool WriteEbmlHeader(IMkvWriter* writer);
 
 // Copies in Chunk from source to destination between the given byte positions