Add size_on_disk to getblockchaininfo from BTC master

src/main.h

@@ -916,6 +916,8 @@ extern CBlockTreeDB *pblocktree;
  */
 int GetSpendHeight(const CCoinsViewCache& inputs);
 
+uint64_t CalculateCurrentUsage();
+
 /** Return a CMutableTransaction with contextual default values based on set of consensus rules at height */
 CMutableTransaction CreateNewContextualCMutableTransaction(const Consensus::Params& consensusParams, int nHeight);