Hoist style-related context bits into style/.

We do a few things-here:
* Hoist non-layout-dependent fields in SharedLayoutData and LocalLayoutData into style/.
* Hoist parts of css/matching.rs into style/.
* Hoist parts of layout/animation.rs into style/animation.rs.
* Remove the duplicated-but-slightly-different definition of OpaqueNode.

components/style/context.rs

@@ -0,0 +1,74 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use animation::Animation;
+use app_units::Au;
+use dom::OpaqueNode;
+use euclid::Size2D;
+use matching::{ApplicableDeclarationsCache, StyleSharingCandidateCache};
+use msg::ParseErrorReporter;
+use selector_matching::Stylist;
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::sync::mpsc::Sender;
+use std::sync::{Arc, Mutex, RwLock};
+
+pub struct StylistWrapper(pub *const Stylist);
+
+// FIXME(#6569) This implementation is unsound.
+#[allow(unsafe_code)]
+unsafe impl Sync for StylistWrapper {}
+
+pub struct SharedStyleContext {
+    /// The current viewport size.
+    pub viewport_size: Size2D<Au>,
+
+    /// Screen sized changed?
+    pub screen_size_changed: bool,
+
+    /// The CSS selector stylist.
+    ///
+    /// FIXME(#2604): Make this no longer an unsafe pointer once we have fast `RWArc`s.
+    pub stylist: StylistWrapper,
+
+    /// Starts at zero, and increased by one every time a layout completes.
+    /// This can be used to easily check for invalid stale data.
+    pub generation: u32,
+
+    /// A channel on which new animations that have been triggered by style recalculation can be
+    /// sent.
+    pub new_animations_sender: Mutex<Sender<Animation>>,
+
+    /// Why is this reflow occurring
+    pub goal: ReflowGoal,
+
+    /// The animations that are currently running.
+    pub running_animations: Arc<RwLock<HashMap<OpaqueNode, Vec<Animation>>>>,
+
+    /// The list of animations that have expired since the last style recalculation.
+    pub expired_animations: Arc<RwLock<HashMap<OpaqueNode, Vec<Animation>>>>,
+
+    ///The CSS error reporter for all CSS loaded in this layout thread
+    pub error_reporter: Box<ParseErrorReporter + Sync>,
+}
+
+pub struct LocalStyleContext {
+    pub applicable_declarations_cache: RefCell<ApplicableDeclarationsCache>,
+    pub style_sharing_candidate_cache: RefCell<StyleSharingCandidateCache>,
+}
+
+pub trait StyleContext<'a> {
+    fn shared_context(&self) -> &'a SharedStyleContext;
+    fn local_context(&self) -> &LocalStyleContext;
+}
+
+/// Why we're doing reflow.
+#[derive(PartialEq, Copy, Clone, Debug)]
+pub enum ReflowGoal {
+    /// We're reflowing in order to send a display list to the screen.
+    ForDisplay,
+    /// We're reflowing in order to satisfy a script query. No display list will be created.
+    ForScriptQuery,
+}
+