Add Servo

[jugglinmike]

Add Servo, the new Mozilla browser engine https://servo.org/

Originally requested via gh-831

[afmenez]

I don't see the point, Servo is an experimental browser for testing purposes, it is not supposed to be used by end users. Besides that, it uses the same JavaScript engine as Firefox.

[jugglinmike]

This was discussed in the issue referenced above, but my comment got a little
buried. Here's the rationale:

It's true that the Servo project does not itself implement an ECMAScript
engine, but it does include one--SpiderMonkey. This is analogous for the V8
engine: both Chrome and Node.js are listed in the table because, although
they both embed the same engine, the details of embedding can have observable
effects on the runtime behavior. Likewise, Firefox's presence in the table
does not fully account for Servo.

[afmenez]

My main argument is that Servo is not a real browser, has no real users, and is not worth the hassle of maintaining its results on the table.

[chicoxyzzy]

Any objections against closing this issue?