Auto merge of #17974 - froydnj:remove-testing-feature, r=SimonSapin

remove testing feature from stylo_tests

`stylo_tests` currently requires a separate version of the `style` crate, compiled with the `testing` feature, so a function testing the size of specified values can be accessed.  With a few tweaks, we can make the information needed for the test available to the `stylo_tests` crate directly, eliminating the need for a separately-compiled `style` crate.

This doesn't matter much for Servo itself (it might make CI times slightly faster?), but Gecko automation/development would like to run `stylo_tests`, and not having to compile two versions of the `style` crate (or have a dead, test-only function hanging around in the `style` crate) would be a win.

---

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] There are tests for these changes

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17974)
<!-- Reviewable:end -->

tests/unit/style/Cargo.toml

@@ -9,9 +9,6 @@ name = "style_tests"
 path = "lib.rs"
 doctest = false
 
-[features]
-testing = ["style/testing"]
-
 [dependencies]
 byteorder = "1.0"
 app_units = "0.5"

tests/unit/style/lib.rs

@@ -19,7 +19,7 @@ extern crate servo_atoms;
 extern crate servo_config;
 extern crate servo_url;
 #[macro_use] extern crate size_of_test;
-extern crate style;
+#[macro_use] extern crate style;
 extern crate style_traits;
 extern crate test;
 
@@ -32,6 +32,8 @@ mod parsing;
 mod properties;
 mod rule_tree;
 mod size_of;
+#[path = "../stylo/specified_values.rs"]
+mod specified_values;
 mod str;
 mod stylesheets;
 mod stylist;

tests/unit/style/size_of.rs

@@ -12,8 +12,3 @@ size_of_test!(test_size_of_property_declaration, properties::PropertyDeclaration
 // This is huge, but we allocate it on the stack and then never move it,
 // we only pass `&mut SourcePropertyDeclaration` references around.
 size_of_test!(test_size_of_parsed_declaration, properties::SourcePropertyDeclaration, 576);
-
-#[test]
-fn size_of_specified_values() {
-    ::style::properties::test_size_of_specified_values();
-}