code: function parsePackStyle(file, context, opts) {
      var content = file.getContent();
      var packStyleFiles = [];
  
      content = _.parseHtmlStyle(content, function (found) {
          var match = found.match;
  
          if (found.isStyleLink) {
              var styleFile = context.getFileByUrl(found.href, file);
              if (styleFile && opts.packCss) {
                  packStyleFiles.push({
                      file: styleFile,
                      raw: match,
                      attrs: found.attrs
                  });
              }
          }
  
          return match;
      });
  
      if (packStyleFiles.length
          && !~content.indexOf(opts.stylePlaceholder)
          && opts.autoInsertPlaceholder
      ) {
          var lastStyle = packStyleFiles[packStyleFiles.length - 1].raw;
          content = content.replace(lastStyle, lastStyle + opts.stylePlaceholder);
      }
      file.setContent(content);
      file._initStylePlacedholder = true;
      return packStyleFiles;
  }
docs: 解析 html 文件要打包的样式，并插入后续要插入的样式占位符，如果有必要的话
  
  @param {File} file html 文件
  @param {Context} context 上下文对象
  @param {Object} opts 解析选项
  @return {Array.<Object>}