Google has decided to block Flash ads on all websites by 1st September, following the example of Mozilla. If a user wishes to "unfreeze" it, he can make right-click and choose to play the plugin.
The "freezing" does not cover important material with Flash, but only ads. This means that it will continue to operate normally embedded Flash Players for videos, but it will stop the annoying ads.
Google automatically converts the Flash loaded on Adwords ads to HTML5. In different platforms, you'll have to do the conversion.
Google blocks Adobe Flash Player not only for security, but also because it is a heavy load operation in Chrome, something that has an impact on the performance of the devices. Also, one of the main reasons are to save energy, as the auto-play Flash quickly reduce the battery of a laptop.