Rename CSSPseudoElement.parentElement to CSSPseudoElement.element

As per CSSWG resolution:

  w3c/csswg-drafts#2816 (comment)

And corresponding spec change:

  w3c/csswg-drafts@2dbf1e4

Differential Revision: https://phabricator.services.mozilla.com/D20427

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1528883
gecko-commit: f35e52301a453825fbe63b074b7702968786d8fe
gecko-integration-branch: central
gecko-reviewers: bzbarsky

css/css-animations/Element-getAnimations.tentative.html

@@ -374,12 +374,12 @@
   assert_equals(animations[1].effect.target.type, '::before',
                 'The animation targeting the ::before pseudo-element ' +
                 'should be returned second');
-  assert_equals(animations[1].effect.target.parentElement, parent,
+  assert_equals(animations[1].effect.target.element, parent,
                 'This ::before element should be child of parent element');
   assert_equals(animations[2].effect.target.type, '::after',
                 'The animation targeting the ::after pesudo-element ' +
                 'should be returned third');
-  assert_equals(animations[2].effect.target.parentElement, parent,
+  assert_equals(animations[2].effect.target.element, parent,
                 'This ::after element should be child of parent element');
 
   assert_equals(animations[3].effect.target, child,
@@ -388,12 +388,12 @@
   assert_equals(animations[4].effect.target.type, '::before',
                 'The animation targeting the ::before pseudo-element ' +
                 'should be returned fifth');
-  assert_equals(animations[4].effect.target.parentElement, child,
+  assert_equals(animations[4].effect.target.element, child,
                 'This ::before element should be child of child element');
   assert_equals(animations[5].effect.target.type, '::after',
                 'The animation targeting the ::after pesudo-element ' +
                 'should be returned last');
-  assert_equals(animations[5].effect.target.parentElement, child,
+  assert_equals(animations[5].effect.target.element, child,
                 'This ::after element should be child of child element');
 }, '{ subtree: true } on an element with a child returns animations from the'
    + ' element, its pseudo-elements, its child and its child pseudo-elements');

web-animations/animation-model/animation-types/property-list.js

@@ -1445,7 +1445,7 @@ const gCSSProperties = {
 function testAnimationSamples(animation, idlName, testSamples) {
   const type = animation.effect.target.type;
   const target = animation.effect.target.constructor.name === 'CSSPseudoElement'
-                 ? animation.effect.target.parentElement
+                 ? animation.effect.target.element
                  : animation.effect.target;
   for (const testSample of testSamples) {
     animation.currentTime = testSample.time;
@@ -1466,7 +1466,7 @@ function toOrderedArray(string) {
 function testAnimationSamplesWithAnyOrder(animation, idlName, testSamples) {
   const type = animation.effect.target.type;
   const target = animation.effect.target.constructor.name === 'CSSPseudoElement'
-                 ? animation.effect.target.parentElement
+                 ? animation.effect.target.element
                  : animation.effect.target;
   for (const testSample of testSamples) {
     animation.currentTime = testSample.time;