Implement a basic test for Fetch
As per @jdm's suggestion that I start minimally testing the Fetch protocol to catch any errors, I wrote a very simple test that just calls Fetch and checks that the response isn't a network error. I've made changes as necessary for every failure I encountered, although this doesn't mean the implementation is faultless yet.
As always, I look forward to any feedback for improvements regarding the test itself, the changes to the fetch files I've made, and anything that I missed and should update.
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The pipeline id stuff is currently unused. If someone needs it, they can add
an additional trait bound on their css error reporter to get the pipeline id.
Fix `linear_gradients_lengths_a.html` and fix Servo's use of "background-clip" to actually make it work.
See the commit messages for details.
r? @mbrubeck
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Correctly handle local sources for CSS3 fonts
Currently, servo panics for me when loading something like this:
```
@font-face {
font-family: "test family";
src: local(test font face);
}
```
That's due to a bug in `FontCacheTask`. `FontCacheTask` tries to get the value for the key
"test font face" from `self.web_families`, but previously initialized a value for the key "test family".
These two commits add an awkward test and fix the bug by not shadowing the variable `family_name`. Since the argument to `local()` should explicitly not be the name of a font family, the previous variable name was wrong and misleading anyways.
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Implement EventSource and update test expectations
Partial #8925.
Most of the processing model for `EventSource` are unimplemented because we currently don't have a fetch implementation.
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`linear_gradients_lengths_ref.html` use `background-clip: content-box`.
The tests clearly expect the background painting area to have width of
100px, but since the default value of `background-clip` is `border-box`
and the boxes in question have a 1-pixel border the background painting
areas are actually 102px. This commit fixes the tests so that the width
of the background painting area is actually 100px.
This test tries to add a web font to the `FontCacheTask`. The added web font
corresponds to the following CSS font definition:
```
@font-face {
font-family: "test family";
src: local(test font face);
}
```
This test fails, since `FontCacheTask` tries to get the value for the key
"test font face" from `self.web_families`, but previously initialized
a value for the key "test family".
