anchor.diff:  
   import 'package:grinder/grinder.dart';
   import 'package:intl/intl.dart';
  -import 'package:polymer/builder.dart' as polymer;
   
   final NumberFormat _NF = new NumberFormat.decimalPattern();
   
  
positive.code: void clean(GrinderContext context) {
    // delete the sdk directory
    runCommandSync(context, 'rm -rf app/sdk/lib');
    runCommandSync(context, 'rm app/sdk/version');
  
    // delete any compiled js output
    runCommandSync(context, 'rm app/*.dart.js');
    runCommandSync(context, 'rm app/*.dart.precompiled.js');
    runCommandSync(context, 'rm app/*.js.map');
    runCommandSync(context, 'rm app/*.js.deps');
  
    // TODO: delete the build/ dir?
  
  
negative.code:   runCommandSync(context, 'rm -rf build/chrome-app/spark/spark_test.dart');
  
    // zip spark.zip . -r -q -x .*
    runCommandSync(context, 'zip ../../../dist/spark.zip . -qr -x .*',
        cwd: 'build/chrome-app/spark');
    printSize(context, new File('dist/spark.zip'));
  }
  
  