code: function initDirFiles(dir, cache) {
      let cacheDirFiles = {};
      cache.setDirFileListInfo(dir, cacheDirFiles);
  
      let files = fs.readdirSync(dir);
      for (let i = 0, len = files.length; i < len; i++) {
          let file = files[i];
          let fullPath = path.resolve(dir, file);
  
          let stat = getFileState(fullPath);
          if (!stat || stat.isDirectory()) {
              continue;
          }
  
          let fileName = getFileName(fullPath);
          let fileList = cacheDirFiles[fileName];
          if (!fileList) {
              fileList = cacheDirFiles[fileName] = [];
          }
          fileList.push(fullPath);
      }
  
      return cacheDirFiles;
  }
docs: Initialize the file list information in the given directory.
  Return the file info structure:
  {
  'fileName1': ['fullPath11', 'fullPath12'],
  'fileName2': ['fullPath21', 'fullPath22']'
  }
  
  e.g., the dir `/test/src` has files: `/test/src/a.js`, `/test/src/a.css`
  then response:
  {
  'a': ['/test/src/a.js', '/test/src/a.css']
  }
  
  @inner
  @param {string} dir the directory to init
  @param {CacheManager} cache the cache manager
  @return {Object}