With the ‘Detect and run important Plugin content’ set as default in the Chrome browser, the flash content smaller than 400px width or 300px height will be automatically paused, however, this doesn’t apply to the plugin content smaller than 5 x 5 or smaller or undefined size. From Chrome 53 onwards, Google to remove this exception, which means flash will be fully blocked by default. And in this December 2016, HTML5 will be made as the default experience in Chrome 55, except for sites which only supports flash. For those sites, first visits to site will prompt the user to enable flash.

Check this post for Google announcement on this.