Personally I think it is like a good manner to always add width and height attributes to img elements on point where the img-element is generated. That is the place where I might know for sure which exact image-file I’m putting in. CSS is far away from the actual image-file.
On top the browsers use this extra info about the image size to calculate aspect-ratio before loading the image file - and before CSS parsing.
For this case the emojis are used in many different places - and sometimes defining sizes via CSS will be skipped accidentally.
E.g. see crawler view of this very same topic on PageSpeed
我个人认为，在生成 img 元素时，始终为其添加 width 和 height 属性是一种良好的习惯。因为那是唯一能确切知道我将放入哪个图像文件的地方。CSS 距离实际的图像文件很远。
此外，浏览器在加载图像文件和解析 CSS 之前，会利用关于图像大小的这些额外信息来计算 aspect-ratio。
在这种情况下，表情符号在许多不同的地方使用——有时会意外地跳过通过 CSS 定义大小。
例如，请参阅此关于 PageSpeed 的相同主题的爬虫视图。