Some tabs in Chrome Task Manager are linked together so I can forceclose them all or none at one time. I can't kill just one of them. Do you know why is that?
And it's not like only JIRA tabs are connected. I've seen many cases with Facebook and other sites linked like this.
From Chromium Process Models (emphasis mine):
By default, Chromium creates a renderer process for each instance of a site the user visits. This ensures that pages from different sites are rendered independently, and that separate visits to the same site are also isolated from each other. Thus, failures (e.g., renderer crashes) or heavy resource usage in one instance of a site will not affect the rest of the browser. This model is based on both the origin of the content and relationships between tabs that might script each other. As a result, two tabs may display pages that are rendered in the same process, while navigating to a cross-site page in a given tab may switch the tab's rendering process.
A "site instance" is a collection of connected pages from the same site. We consider two pages as connected if they can obtain references to each other in script code (e.g., if one page opened the other in a new window using Javascript)
--process-per-tab. Chromium Process Models (from answer, below) has been updated since this question was asked.