servo: Merge #17758 - Bug 1377993: Make node slots less memory hungry in common cases (from emilio:extended-slots); r=heycam

Source-Repo: https://github.com/servo/servo
Source-Revision: 3459748134e14dd2265e8b94b43bff18a02c042d

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 95bf4decec3c47840604cc82912f49ec984dc481

servo/components/style/gecko/wrapper.rs

@@ -505,7 +505,7 @@ impl<'le> GeckoElement<'le> {
 
     /// Returns true if this element has a shadow root.
     fn has_shadow_root(&self) -> bool {
-        self.get_dom_slots().map_or(false, |slots| !slots.mShadowRoot.mRawPtr.is_null())
+        self.get_extended_slots().map_or(false, |slots| !slots.mShadowRoot.mRawPtr.is_null())
     }
 
     /// Returns a reference to the DOM slots for this Element, if they exist.
@@ -514,6 +514,13 @@ impl<'le> GeckoElement<'le> {
         unsafe { slots.as_ref() }
     }
 
+    /// Returns a reference to the extended DOM slots for this Element.
+    fn get_extended_slots(&self) -> Option<&structs::FragmentOrElement_nsExtendedDOMSlots> {
+        self.get_dom_slots().and_then(|s| {
+            unsafe { s.mExtendedSlots.mPtr.as_ref() }
+        })
+    }
+
     #[inline]
     fn get_xbl_binding(&self) -> Option<GeckoXBLBinding> {
         if self.flags() & (structs::NODE_MAY_BE_IN_BINDING_MNGR as u32) == 0 {
@@ -556,10 +563,9 @@ impl<'le> GeckoElement<'le> {
 
     fn get_non_xul_xbl_binding_parent_raw_content(&self) -> *mut nsIContent {
         debug_assert!(!self.is_xul_element());
-        match self.get_dom_slots() {
-            Some(slots) => unsafe { *slots.__bindgen_anon_1.mBindingParent.as_ref() },
-            None => ptr::null_mut(),
-        }
+        self.get_extended_slots().map_or(ptr::null_mut(), |slots| {
+            slots.mBindingParent
+        })
     }
 
     fn has_xbl_binding_parent(&self) -> bool {