SRI: Add tests for <link> elements

[metromoxie]

This adds element tests equivalent to the already present (and valid) <script> tests. @hillbrad, can you take a look? Also, a sanity check from @devd, @mozfreddyb, or @fmarier would be appreciated.

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/5309

This is an external review system which you may optionally use for the code review of your pull request.

In order to help critic track your changes, please do not make in-place history rewrites (e.g. via git rebase -i or git commit --amend) when updating this pull request.

[jgraham]

Note: in the future please don't merge master into your branches, instead please rebase your branch onto master if it conflicts with other changes.

[jgraham]

(the reason for this is that this kind of merge makes the history confusing and, in this case, people were worried you had accidentally clobbered some upstream changes)

[metromoxie]

Okay, good to know. That's what I usually do, but hoppipolla-critic-bot seems to say that is frowned upon. Is there a nuance I'm missing, or is the bot just wrong? Thanks!

[jgraham]

Right, so it's always OK to rebase after you have your review accepted because at that point critic no longer cares. If you need to rebase for some reason whilst review is ongoing you need to do only a move-type rebase (i.e. don't squash or push extra stuff) and then tell critic about the rebase (there's a button on the review page) before you push anything else.

Unfortunately critic isn't the best when it comes to handling rebases.

[metromoxie]

Got it. Thanks!