old_contents: var path = require('path');
  var fs   = require('fs');
  
  var assetRev = require('./asset-rev');
  
  function EmberCLIAssetRev(project) {
    this.project = project;
    this.name    = 'broccoli-asset-rev';
  }
  
  EmberCLIAssetRev.prototype.initializeOptions = function() {
    var defaultOptions = {
      enabled: this.app.env === 'production',
      exclude: [],
      extensions: ['js', 'css', 'png', 'jpg', 'gif'],
      prepend: '',
      replaceExtensions: ['html', 'css', 'js']
    }
  
    this.options = this.app.options.fingerprint = this.app.options.fingerprint || {};
  
    for (var option in defaultOptions) {
      if (!this.options.hasOwnProperty(option)) {
        this.options[option] = defaultOptions[option];
      }
    }
  };
  
  EmberCLIAssetRev.prototype.postprocessTree = function (type, tree) {
    if (type === 'all' && this.options.enabled) {
      tree = assetRev(tree, this.options);
    }
  
    return tree;
  };
  
  EmberCLIAssetRev.prototype.included = function (app) {
    this.app = app;
    this.initializeOptions();
  };
  
  module.exports = EmberCLIAssetRev;
  
new_contents: var path = require('path');
  var fs   = require('fs');
  
  var assetRev = require('./asset-rev');
  
  function EmberCLIAssetRev(project) {
    this.project = project;
    this.name    = 'broccoli-asset-rev';
  }
  
  EmberCLIAssetRev.prototype.initializeOptions = function() {
    var defaultOptions = {
      enabled: this.app.env === 'production',
      exclude: [],
      extensions: ['js', 'css', 'png', 'jpg', 'gif'],
      prepend: '',
      replaceExtensions: ['html', 'css', 'js']
    }
  
    this.options = this.app.options.fingerprint = this.app.options.fingerprint || {};
  
    for (var option in defaultOptions) {
      if (!this.options.hasOwnProperty(option)) {
        this.options[option] = defaultOptions[option];
      }
    }
  };
  
  EmberCLIAssetRev.prototype.postprocessTree = function (type, tree) {
    if (type === 'all' && this.options.enabled) {
      tree = assetRev(tree, this.options);
    }
  
    return tree;
  };
  
  EmberCLIAssetRev.prototype.included = function (app) {
    this.app = app;
    this.initializeOptions();
  };
  
  EmberCLIAssetRev.prototype.treeFor = function() {};
  
  module.exports = EmberCLIAssetRev;
  
subject: Implement treeFor method