Auto merge of #29839 - stshine:collapse-through, r=mrobinson

layout_2020: Allow end margin to collapse with children if height is set to 0

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Previously, end margin was allowed to collapse only when block size is not set.

---
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- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [x] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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components/layout_2020/flow/mod.rs

@@ -482,7 +482,7 @@ fn layout_in_flow_non_replaced_block_level(
     let end_margin_can_collapse_with_children = block_is_same_formatting_context &&
         pbm.padding.block_end == Length::zero() &&
         pbm.border.block_end == Length::zero() &&
-        block_size == LengthOrAuto::Auto &&
+        block_size.auto_is(|| Length::zero()) == Length::zero() &&
         min_box_size.block == Length::zero();
 
     let mut clearance = Length::zero();

tests/wpt/metadata-layout-2020/css/CSS2/margin-padding-clear/margin-collapse-016.xht.ini

@@ -1,2 +0,0 @@
-[margin-collapse-016.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/margin-padding-clear/margin-collapse-019.xht.ini

@@ -1,2 +0,0 @@
-[margin-collapse-019.xht]
-  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/normal-flow/margin-collapse-through-zero-height-block.html.ini

@@ -1,2 +0,0 @@
-[margin-collapse-through-zero-height-block.html]
-  expected: FAIL