Reduce the number of places where we need to enumerate ValidationData members.

MozReview-Commit-ID: 9m2ebknBFSE

components/style/context.rs

@@ -463,7 +463,7 @@ impl<E: TElement> ThreadLocalStyleContext<E> {
         self.current_element_info = Some(CurrentElementInfo {
             element: element.as_node().opaque(),
             is_initial_style: !data.has_styles(),
-            validation_data: ValidationData::new(),
+            validation_data: ValidationData::default(),
             possibly_expired_animations: Vec::new(),
         });
     }

components/style/sharing/mod.rs

@@ -16,6 +16,7 @@ use properties::ComputedValues;
 use selectors::bloom::BloomFilter;
 use selectors::matching::{ElementSelectorFlags, StyleRelations};
 use smallvec::SmallVec;
+use std::mem;
 use std::ops::Deref;
 use stylist::{ApplicableDeclarationBlock, Stylist};
 
@@ -36,7 +37,7 @@ pub enum StyleSharingBehavior {
 
 /// Some data we want to avoid recomputing all the time while trying to share
 /// style.
-#[derive(Debug)]
+#[derive(Debug, Default)]
 pub struct ValidationData {
     /// The class list of this element.
     ///
@@ -53,23 +54,9 @@ pub struct ValidationData {
 }
 
 impl ValidationData {
-    /// Trivially construct an empty `ValidationData` with nothing on
-    /// it.
-    pub fn new() -> Self {
-        Self {
-            class_list: None,
-            pres_hints: None,
-            revalidation_match_results: None,
-        }
-    }
-
     /// Move the cached data to a new instance, and return it.
     pub fn take(&mut self) -> Self {
-        Self {
-            class_list: self.class_list.take(),
-            pres_hints: self.pres_hints.take(),
-            revalidation_match_results: self.revalidation_match_results.take(),
-        }
+        mem::replace(self, Self::default())
     }
 
     /// Get or compute the list of presentational attributes associated with
@@ -189,7 +176,7 @@ impl<E: TElement> StyleSharingTarget<E> {
     pub fn new(element: E) -> Self {
         Self {
             element: element,
-            validation_data: ValidationData::new(),
+            validation_data: ValidationData::default(),
         }
     }
 
@@ -242,8 +229,6 @@ impl<E: TElement> StyleSharingTarget<E> {
         data: &mut ElementData)
         -> StyleSharingResult
     {
-        use std::mem;
-
         let shared_context = &context.shared;
         let selector_flags_map = &mut context.thread_local.selector_flags;
         let bloom_filter = context.thread_local.bloom_filter.filter();
@@ -256,12 +241,9 @@ impl<E: TElement> StyleSharingTarget<E> {
                                      &mut self,
                                      data);
 
-        mem::swap(&mut self.validation_data,
-                  &mut context
-                      .thread_local
-                      .current_element_info.as_mut().unwrap()
-                      .validation_data);
 
+        context.thread_local.current_element_info.as_mut().unwrap().validation_data =
+            self.validation_data.take();
         result
     }
 }