style: Add a StylesheetLoader abstraction, and make it a no-op on Geckolib.

Servo doesn't compile at this stage.

tests/unit/style/media_queries.rs

@@ -29,7 +29,8 @@ fn test_media_rule<F>(css: &str, callback: F) where F: Fn(&MediaList, &str) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let stylesheet = Stylesheet::from_str(
         css, url, Origin::Author, Default::default(),
-        Box::new(CSSErrorReporterTest), ParserContextExtraData::default());
+        None, Box::new(CSSErrorReporterTest),
+        ParserContextExtraData::default());
     let mut rule_count = 0;
     media_queries(&stylesheet.rules.read().0, &mut |mq| {
         rule_count += 1;
@@ -53,7 +54,8 @@ fn media_query_test(device: &Device, css: &str, expected_rule_count: usize) {
     let url = ServoUrl::parse("http://localhost").unwrap();
     let ss = Stylesheet::from_str(
         css, url, Origin::Author, Default::default(),
-        Box::new(CSSErrorReporterTest), ParserContextExtraData::default());
+        None, Box::new(CSSErrorReporterTest),
+        ParserContextExtraData::default());
     let mut rule_count = 0;
     ss.effective_style_rules(device, |_| rule_count += 1);
     assert!(rule_count == expected_rule_count, css.to_owned());

tests/unit/style/stylesheets.rs

@@ -52,6 +52,7 @@ fn test_parse_stylesheet() {
         }";
     let url = ServoUrl::parse("about::test").unwrap();
     let stylesheet = Stylesheet::from_str(css, url.clone(), Origin::UserAgent, Default::default(),
+                                          None,
                                           Box::new(CSSErrorReporterTest),
                                           ParserContextExtraData::default());
     let mut namespaces = Namespaces::default();
@@ -332,7 +333,9 @@ fn test_report_error_stylesheet() {
 
     let errors = error_reporter.errors.clone();
 
-    Stylesheet::from_str(css, url, Origin::UserAgent, Default::default(), error_reporter,
+    Stylesheet::from_str(css, url, Origin::UserAgent, Default::default(),
+                         None,
+                         error_reporter,
                          ParserContextExtraData::default());
 
     let mut errors = errors.lock().unwrap();

tests/unit/style/viewport.rs

@@ -25,6 +25,7 @@ macro_rules! stylesheet {
             ServoUrl::parse("http://localhost").unwrap(),
             Origin::$origin,
             Default::default(),
+            None,
             $error_reporter,
             ParserContextExtraData::default()
         ))

tests/unit/stylo/lib.rs

@@ -16,5 +16,8 @@ extern crate style_traits;
 
 mod sanity_checks;
 
+#[path = "../../../ports/geckolib/stylesheet_loader.rs"]
+mod stylesheet_loader;
+
 mod servo_function_signatures;