Bug 1317016 - Basic infrastructure for RestyleHint-driven traversal.

MozReview-Commit-ID: 7wH5XcILVmX

components/style/context.rs

@@ -38,6 +38,14 @@ pub struct SharedStyleContext {
     /// Screen sized changed?
     pub screen_size_changed: bool,
 
+    /// Skip the root during traversal?
+    ///
+    /// This is used in Gecko to style newly-appended children without restyling
+    /// the parent. It would be cleaner to add an API to allow us to enqueue the
+    /// children directly from glue.rs.
+    #[cfg(feature = "gecko")]
+    pub skip_root: bool,
+
     /// The CSS selector stylist.
     pub stylist: Arc<Stylist>,