Blockly.Dart['math_change'] = function(block) {
  // Add to a variable in place.
  var argument0 = Blockly.Dart.valueToCode(block, 'DELTA',
      Blockly.Dart.ORDER_ADDITIVE) || '0';
  var varName = Blockly.Dart.variableDB_.getName(block.getFieldValue('VAR'),