Fix a bunch of clippy lints
This fixes about 130 clippy lints. Let me know if i should split up the commit.
I wasn't sure about some of the changes, especially map_or instead of map(...).unwrap_or(...) and if let instead of single arm match were not always a strict improvement in my opinion, but i'll leave that decision to the reviewer :)
There are about 150 lints left which i thought were clippy bugs or i didn't know how to fix.
cc @Manishearth
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/9123)
<!-- Reviewable:end -->
Support empty strings as the repeat argument (CreatePattern)
According to the third step in the specification [1], createPattern
should let the repetition argument be "repeat" when it is the empty
string.
The code in CanvasRenderingContext2D::CreatePattern did not implement
this step and instead threw a SyntaxError exception when an empty
string was supplied as the repetition argument.
Fixes#9079.
[1] https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/9109)
<!-- Reviewable:end -->
Add 5 different task source channels
This is **not** complete. I really need feedback right away since I felt that the direction I'm heading is very wrong.
Partial #7959.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8871)
<!-- Reviewable:end -->
Split http_loader::load into two methods
This is intended to fix#8976 by moving the http_loader::load code that deals with getting a response and moving it into its own function. I've built it and run existing tests against my changes and that looks fine. I'd like feedback on changes I've made to accommodate refactoring the code. And I'm sure there's a more descriptive function name than "load_response", I just wasn't sure how to describe what it does.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/9078)
<!-- Reviewable:end -->
According to the third step in the specification [1], createPattern
should let the repetition argument be "repeat" when it is the empty
string.
The code in CanvasRenderingContext2D::CreatePattern did not implement
this step and instead threw a SyntaxError exception when an empty
string was supplied as the repetition argument.
Fixes#9079.
[1] https://html.spec.whatwg.org/multipage/#dom-context-2d-createpattern
Enabled use of FontFamily enum type
https://github.com/servo/servo/issues/8371
In addition to replacing loose strings with the FontFamily enum in `font_cache_task.rs`, I also centralized the add_generic_font calls into one single function. If centralizing into one function is not desired or if anything else needs to be changed, please let me know.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8420)
<!-- Reviewable:end -->
… in order to pick up https://github.com/tomaka/glutin/pull/679, which will hopefully get rid of the `[glutin] x error code=8 major=42 minor=0!` messages printed on stdout.
