Refactor style to be completely backend-independent

This commit refactors the style crate to be completely independent of
the actual implementation and pseudo-elements supported.

This also adds a gecko backend which introduces parsing for the
anonymous box pseudo-elements[1], although there's still no way of
querying them.

https://mxr.mozilla.org/mozilla-central/source/layout/style/nsCSSAnonBoxList.h

components/script/Cargo.toml

@@ -81,7 +81,7 @@ num = "0.1.24"
 rand = "0.3"
 ref_slice = "0.1.0"
 rustc-serialize = "0.3"
-selectors = {version = "0.4.2", features = ["heap_size"]}
+selectors = {version = "0.5", features = ["heap_size"]}
 serde = "0.6"
 smallvec = "0.1"
 string_cache = {version = "0.2.9", features = ["heap_size", "unstable"]}

components/script/dom/document.rs

@@ -105,7 +105,7 @@ use std::sync::Arc;
 use string_cache::{Atom, QualName};
 use style::context::ReflowGoal;
 use style::restyle_hints::ElementSnapshot;
-use style::stylesheets::Stylesheet;
+use style::servo::Stylesheet;
 use time;
 use url::{Host, Url};
 use util::str::{DOMString, split_html_space_chars, str_join};

components/script/dom/htmllinkelement.rs

@@ -36,7 +36,8 @@ use std::mem;
 use std::sync::{Arc, Mutex};
 use string_cache::Atom;
 use style::media_queries::{MediaQueryList, parse_media_query_list};
-use style::stylesheets::{Origin, Stylesheet};
+use style::servo::Stylesheet;
+use style::stylesheets::Origin;
 use url::Url;
 use util::str::{DOMString, HTML_SPACE_CHARACTERS};
 

components/script/dom/htmlmetaelement.rs

@@ -15,7 +15,8 @@ use dom::virtualmethods::VirtualMethods;
 use std::ascii::AsciiExt;
 use std::sync::Arc;
 use string_cache::Atom;
-use style::stylesheets::{CSSRule, Origin, Stylesheet};
+use style::servo::Stylesheet;
+use style::stylesheets::{CSSRule, Origin};
 use style::viewport::ViewportRule;
 use util::str::{DOMString, HTML_SPACE_CHARACTERS};
 

components/script/dom/htmlstyleelement.rs

@@ -17,7 +17,8 @@ use layout_interface::{LayoutChan, Msg};
 use std::sync::Arc;
 use string_cache::Atom;
 use style::media_queries::parse_media_query_list;
-use style::stylesheets::{Origin, Stylesheet};
+use style::servo::Stylesheet;
+use style::stylesheets::Origin;
 use util::str::DOMString;
 
 #[dom_struct]

components/script/layout_interface.rs

@@ -24,7 +24,7 @@ use std::sync::mpsc::{Receiver, Sender, channel};
 use string_cache::Atom;
 use style::context::ReflowGoal;
 use style::selector_impl::PseudoElement;
-use style::stylesheets::Stylesheet;
+use style::servo::Stylesheet;
 use url::Url;
 use util::ipc::OptionalOpaqueIpcSender;