Exempt tabs from container rechecking when they are opened from the same host

[blackhole89]

Right now, while the exemption mechanism ensures that you can freely follow links within a domain that has been opened in a different container from the one that it has been assigned to "Always (...) Open in (...)", it does not work when you middle-click to open a link in a new tab. The result is that, for instance, when using containers to log into a website such as github with a nonstandard account while also using middle-click to open new tabs frequently, the user experience is terrible (you get redirected to the confirmation page every single time). (This is exacerbated by the confirmation page interacting badly with addons such as Tree Style Tab.)

Since, as far as I can tell, there is no compelling privacy scenario requiring that you reobtain the user's consent to use nonstandard container C when following a link on host X to open a new tab on the same host (and, as far as I can tell, this is the only class of scenarios in which originUrl and newUrl are on the same host, the active container is not standard for that host and the exemption flag is not set), I propose the following hopefully self-explanatory code fragment to make it so that requests within the same domain always go through and result in a container exemption being set for the tab.

[maxxcrawford]

@blackhole89 Can you please provide some testing steps with reproducible links?

[maxxcrawford]

Blocking this review until testing steps are provided. Thanks!

[blackhole89]

What do you mean by reproducible links? I am not sure if this is still current since I made the PR over two years ago, but I think that the issue I experienced would amount to something like:

1. Create two websites under the same domain, say http://test.com/a.html and http://test.com/b.html, with the former containing a link to the latter.
2. Create two containers X and Y.
3. Set test.com to always open in container X.
4. Create a new tab with container Y.
5. Navigate to http://test.com/a.html and confirm that you indeed want to open it in container Y.
6. Middle-click the link to http://test.com/b.html.

Expected behaviour:

A new tab in container Y is created and navigated to http://test.com/b.html.

Actual behaviour:

A new tab in container Y is created and displays the "are you sure you want to open this page in container Y?" confirmation page.