Ele se chama Site Isolation e é um recurso de segurança:
Site Isolation is an optional security feature in Chrome that offers additional protection against some types of security bugs. It makes it harder for untrusted websites to access or steal information from your accounts on other websites.
De acordo com o Chromium.org Site Isolation ajuda a
mitigate attacks that are able to read otherwise inaccessible data within a process, such as speculative side-channel attack techniques like Spectre/Meltdown. Site Isolation reduces the amount of valuable cross-site information in a web page's process, and thus helps limit what an attacker could access.
Além disso, o isolamento do site
offers more protection against a certain type of web browser security bug, called universal cross-site scripting (UXSS). Security bugs of this form would normally let an attacker bypass the Same Origin Policy within the renderer process, though they don't give the attacker complete control over the process.
Problemas atuais incluem Higher overall memory use in Chrome (about 10-12% in Chrome 65 when isolating all sites with many tabs open).
Ele não está habilitado por padrão chrome://flags/#enable-site-per-process
, mas está sendo testado no campo. Você pode desativar, mas não é recomendado chrome://flags/#site-isolation-trial-opt-out
. Se você excluir um subquadro, o processo do site ainda existirá, mas o Isolamento do site para esse site não estará mais ativado.