Bug 513144. Allow nsMediaCache blocks to be owned by multiple streams at the same time. r=doublec

  // block is the earliest in the stream (so the last block will be the

  // least valuable).

  BlockList         mReadaheadBlocks;

  // The list of metadata blocks; the first block is the most recently used

  BlockList         mMetadataBlocks;

  // The list of played-back blocks; the first block is the most recently used

  BlockList         mPlayedBlocks;

  // The last reported estimate of the decoder's playback rate

  PRUint32          mPlaybackBytesPerSecond;

  // The number of times this stream has been Pinned without a