Auto merge of #17469 - nox:empty-vs-initial, r=emilio

Distinguish the emptiness of a property from its initial value

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tests/wpt/metadata-css/css-transitions-1_dev/html/transition-property-002.htm.ini

@@ -6,6 +6,3 @@
   [parse 'all, none']
     expected: FAIL
 
-  [parse 'initial']
-    expected: FAIL
-

tests/wpt/mozilla/meta/MANIFEST.json

@@ -25556,7 +25556,7 @@
    "testharness"
   ],
   "mozilla/calc.html": [
-   "a1f441f7fd4b9ab3ae9e1cb5403cfe8de90bb71c",
+   "5d59d5b367a023e778ce6968acdeca6b8b7c3197",
    "testharness"
   ],
   "mozilla/canvas.initial.reset.2dstate.html": [

tests/wpt/mozilla/tests/mozilla/calc.html

@@ -9,6 +9,7 @@
 #inner {
     border-style: solid; /* So used border == computed border */
     outline-style: solid; /* So used outline-width == computed outline-width */
+    transition-property: none; /* so that tests don't occur in the middle of a transition */
 }
 </style>
 </head>