add timecode_scale element to Cluster

This became a required argument in libwebm:
commit b6311dc16f0c1a0d7b31ac44a44fd96ce7505727
Author: Vignesh Venkatasubramanian <vigneshv@google.com>
Date:   Thu May 7 13:58:33 2015 -0700

    mkvmuxer: Refactor to remove a lot of duplicate code

BUG=webm:1480
2 files changed
tree: 918bf57dc2445cc056dfd631d5193ea6e22849d1
  1. JNI/