CSS: WPT for backdrop-filter inheritance

backdrop-filter does not inherit, and has initial value 'none'.
https://drafts.fxtf.org/filter-effects-2/#BackdropFilterProperty

Change-Id: I245e6586d25787a322532b53c8b96a90de7acfa9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1741432
Auto-Submit: Eric Willigers <[email protected]>
Commit-Queue: Mason Freed <[email protected]>
Reviewed-by: Mason Freed <[email protected]>
Cr-Commit-Position: refs/heads/master@{#684913}

Author: ericwilligers

css/filter-effects/inheritance.html

@@ -4,6 +4,7 @@
 <meta charset="utf-8">
 <title>Inheritance of Filter Effects properties</title>
 <link rel="help" href="https://drafts.fxtf.org/filter-effects/#property-index">
+<link rel="help" href="https://drafts.fxtf.org/filter-effects-2/#property-index">
 <meta name="assert" content="Properties inherit according to the spec.">
 <meta name="assert" content="Properties have initial values according to the spec.">
 <script src="/resources/testharness.js"></script>
@@ -15,6 +16,7 @@
   <div id="target"></div>
 </div>
 <script>
+assert_not_inherited('backdrop-filter', 'none', 'blur(10px)');
 assert_inherited('color-interpolation-filters', 'linearrgb', 'srgb');
 assert_not_inherited('filter', 'none', 'blur(10px)');
 assert_not_inherited('flood-color', 'rgb(0, 0, 0)', 'rgb(42, 53, 64)');