style: Hide LocalMatchingContext.

This type is a lot of complexity related to a very specific thing such as the
hover and active quirk.

Instead of that, move `nesting_level` to `MatchingContext`, and simplify all
this computing whether the quirk applies upfront, for each complex selector we
test.

This is less error-prone, and also allows simplifying more stuff in a bit.

components/layout_thread/dom_wrapper.rs

@@ -51,7 +51,7 @@ use script_layout_interface::{OpaqueStyleAndLayoutData, StyleData};
 use script_layout_interface::wrapper_traits::{DangerousThreadSafeLayoutNode, GetLayoutData, LayoutNode};
 use script_layout_interface::wrapper_traits::{PseudoElementType, ThreadSafeLayoutElement, ThreadSafeLayoutNode};
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint, CaseSensitivity};
-use selectors::matching::{ElementSelectorFlags, LocalMatchingContext, MatchingContext, RelevantLinkStatus};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, RelevantLinkStatus};
 use selectors::matching::VisitedHandlingMode;
 use selectors::sink::Push;
 use servo_arc::{Arc, ArcBorrow};
@@ -720,7 +720,7 @@ impl<'le> ::selectors::Element for ServoLayoutElement<'le> {
 
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
-                                    _: &mut LocalMatchingContext<Self::Impl>,
+                                    _: &mut MatchingContext,
                                     _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool
@@ -1240,7 +1240,7 @@ impl<'le> ::selectors::Element for ServoThreadSafeLayoutElement<'le> {
 
     fn match_non_ts_pseudo_class<F>(&self,
                                     _: &NonTSPseudoClass,
-                                    _: &mut LocalMatchingContext<Self::Impl>,
+                                    _: &mut MatchingContext,
                                     _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool

components/script/dom/element.rs

@@ -89,7 +89,7 @@ use script_layout_interface::message::ReflowGoal;
 use script_thread::ScriptThread;
 use selectors::Element as SelectorsElement;
 use selectors::attr::{AttrSelectorOperation, NamespaceConstraint, CaseSensitivity};
-use selectors::matching::{ElementSelectorFlags, LocalMatchingContext, MatchingContext, RelevantLinkStatus};
+use selectors::matching::{ElementSelectorFlags, MatchingContext, MatchingMode, RelevantLinkStatus};
 use selectors::matching::{HAS_EDGE_CHILD_SELECTOR, HAS_SLOW_SELECTOR, HAS_SLOW_SELECTOR_LATER_SIBLINGS};
 use selectors::sink::Push;
 use servo_arc::Arc;
@@ -2583,7 +2583,7 @@ impl<'a> SelectorsElement for DomRoot<Element> {
 
     fn match_non_ts_pseudo_class<F>(&self,
                                     pseudo_class: &NonTSPseudoClass,
-                                    _: &mut LocalMatchingContext<Self::Impl>,
+                                    _: &mut MatchingContext,
                                     _: &RelevantLinkStatus,
                                     _: &mut F)
                                     -> bool

components/selectors/context.rs

@@ -102,6 +102,9 @@ pub struct MatchingContext<'a> {
     /// See https://drafts.csswg.org/selectors-4/#scope-pseudo
     pub scope_element: Option<OpaqueElement>,
 
+    /// The current nesting level of selectors that we're matching.
+    pub nesting_level: usize,
+
     quirks_mode: QuirksMode,
     classes_and_ids_case_sensitivity: CaseSensitivity,
 }
@@ -140,6 +143,7 @@ impl<'a> MatchingContext<'a> {
             relevant_link_found: false,
             classes_and_ids_case_sensitivity: quirks_mode.classes_and_ids_case_sensitivity(),
             scope_element: None,
+            nesting_level: 0,
         }
     }