code: function runTool(platform, args, done) {
    var inputFile1 = args[0];
    var inputFile2 = args[1];
    var filterString = args[2];
    if (!inputFile1 || !inputFile2) {
      console.log('usage: diff.js file1.wtf-trace file2.wtf-trace [filter]');
      done(1);
      return;
    }
    console.log('Diffing ' + inputFile1 + ' and ' + inputFile2 + '...');
    console.log('');
  
    var filter = null;
    if (filterString) {
      filter = new wtf.db.Filter(filterString);
    }
  
    // Create databases for querying.
    var db1 = null;
    var db2 = null;
    wtf.db.load(inputFile1, function(db) {
      if (db instanceof Error) {
        console.log('ERROR: unable to open ' + inputFile1, db);
        done(1);
        return;
      }
  
      db1 = db;
      if (db1 && db2) {
        diffDatabases(db1, db2, filter);
        done(0);
      }
    });
    wtf.db.load(inputFile2, function(db) {
      if (db instanceof Error) {
        console.log('ERROR: unable to open ' + inputFile2, db);
        done(1);
        return;
      }
  
      db2 = db;
      if (db1 && db2) {
        diffDatabases(db1, db2, filter);
        done(0);
      }
    });
  }
docs: Diff tool.
  @param {!wtf.pal.IPlatform} platform Platform abstraction layer.
  @param {!Array.<string>} args Command line arguments.
  @param {function(number)} done Call to end the program with a return code.