Support text-indent in layout-2020

Existing WPT now passing:
  - css/CSS2/floats-clear/floats-138.xht
  - css/CSS2/text/text-indent-007.xht
  - css/CSS2/text/text-indent-008.xht
  - css/CSS2/text/text-indent-010.xht
  - css/CSS2/text/text-indent-019.xht
  - css/CSS2/text/text-indent-020.xht
  - css/CSS2/text/text-indent-031.xht
  - css/CSS2/text/text-indent-032.xht
  - css/CSS2/text/text-indent-043.xht
  - css/CSS2/text/text-indent-044.xht
  - css/CSS2/text/text-indent-055.xht
  - css/CSS2/text/text-indent-056.xht
  - css/CSS2/text/text-indent-067.xht
  - css/CSS2/text/text-indent-068.xht
  - css/CSS2/text/text-indent-079.xht
  - css/CSS2/text/text-indent-080.xht
  - css/CSS2/text/text-indent-091.xht
  - css/CSS2/text/text-indent-092.xht
  - css/CSS2/text/text-indent-103.xht
  - css/CSS2/text/text-indent-104.xht
  - css/CSS2/text/text-indent-112.xht
  - css/CSS2/text/text-indent-113.xht
  - css/CSS2/text/text-indent-115.xht
  - css/CSS2/text/text-indent-applies-to-002.xht
  - css/CSS2/text/text-indent-applies-to-003.xht
  - css/CSS2/text/text-indent-applies-to-005.xht
  - css/CSS2/text/text-indent-applies-to-006.xht
  - css/CSS2/text/text-indent-applies-to-007.xht
  - css/CSS2/text/text-indent-applies-to-008.xht
  - css/CSS2/text/text-indent-applies-to-009.xht
  - css/CSS2/text/text-indent-applies-to-010.xht
  - css/CSS2/text/text-indent-applies-to-011.xht
  - css/CSS2/text/text-indent-applies-to-014.xht
  - css/CSS2/text/text-indent-applies-to-015.xht
  - css/CSS2/text/text-indent-inherited-001.xht
  - css/CSS2/text/text-indent-overflow-001.xht
  - css/CSS2/text/text-indent-overflow-002.xht
  - css/CSS2/text/text-indent-overflow-003.xht
  - css/CSS2/text/text-indent-overflow-004.xht
  - css/CSS2/text/text-indent-wrap-001.xht
  - css/css-text-decor/text-shadow/textindent.html
  - css/css-text/text-indent/text-indent-percentage-002.html
  - css/css-text/text-indent/text-indent-percentage-003.html
  - css/css-text/text-indent/text-indent-percentage-004.html
  - css/css-values/minmax-length-percent-serialize.html
  - css/css-values/minmax-length-serialize.html

Also improvements in:
  - css/css-text/animations/text-indent-interpolation.html
  - css/css-text/inheritance.html
  - css/css-text/parsing/text-indent-computed.html
  - css/css-text/parsing/text-indent-valid.html
  - css/css-values/animations/calc-interpolation.html
  - css/css-values/minmax-percentage-serialize.html
  - css/css-values/viewport-units-css2-001.html
  - css/cssom/serialize-values.html

Existing WPT now failing, due to lack of direction, flex and grid:
  - css/CSS2/text/text-indent-rtl-001.xht
  - css/CSS2/text/text-indent-rtl-002.xht
  - css/css-text/text-indent/anonymous-flex-item-001.html
  - css/css-text/text-indent/anonymous-grid-item-001.html

This test was already failing due to tabs, but wasn't tracked:
  - css/css-text/text-indent/text-indent-tab-positions-001.html

New WPT tests:
 - css/css-text/text-indent/text-indent-length-001.html
 - css/css-text/text-indent/text-indent-length-002.html
   This one fails in layout-2013.

components/layout_2020/flow/construct.rs

@@ -63,6 +63,7 @@ impl BlockFormattingContext {
         let ifc = InlineFormattingContext {
             inline_level_boxes,
             text_decoration_line,
+            has_first_formatted_line: true,
         };
         let contents = BlockContainer::InlineFormattingContext(ifc);
         let bfc = Self {
@@ -187,7 +188,10 @@ impl BlockContainer {
             context,
             info,
             block_level_boxes: Vec::new(),
-            ongoing_inline_formatting_context: InlineFormattingContext::new(text_decoration_line),
+            ongoing_inline_formatting_context: InlineFormattingContext::new(
+                text_decoration_line,
+                /* has_first_formatted_line = */ true,
+            ),
             ongoing_inline_boxes_stack: Vec::new(),
             anonymous_style: None,
             contains_floats: ContainsFloats::No,
@@ -690,6 +694,8 @@ where
             .is_empty()
         {
             // There should never be an empty inline formatting context.
+            self.ongoing_inline_formatting_context
+                .has_first_formatted_line = false;
             return;
         }
 

components/layout_2020/flow/inline.rs

@@ -35,6 +35,9 @@ use webrender_api::FontInstanceKey;
 pub(crate) struct InlineFormattingContext {
     pub(super) inline_level_boxes: Vec<ArcRefCell<InlineLevelBox>>,
     pub(super) text_decoration_line: TextDecorationLine,
+    // Whether this IFC contains the 1st formatted line of an element
+    // https://www.w3.org/TR/css-pseudo-4/#first-formatted-line
+    pub(super) has_first_formatted_line: bool,
 }
 
 #[derive(Debug, Serialize)]
@@ -130,10 +133,14 @@ struct Lines {
 }
 
 impl InlineFormattingContext {
-    pub(super) fn new(text_decoration_line: TextDecorationLine) -> InlineFormattingContext {
+    pub(super) fn new(
+        text_decoration_line: TextDecorationLine,
+        has_first_formatted_line: bool,
+    ) -> InlineFormattingContext {
         InlineFormattingContext {
             inline_level_boxes: Default::default(),
             text_decoration_line,
+            has_first_formatted_line,
         }
     }
 
@@ -273,7 +280,16 @@ impl InlineFormattingContext {
                 fragments: Vec::new(),
                 next_line_block_position: Length::zero(),
             },
-            inline_position: Length::zero(),
+            inline_position: if self.has_first_formatted_line {
+                containing_block
+                    .style
+                    .get_inherited_text()
+                    .text_indent
+                    .to_used_value(containing_block.inline_size.into())
+                    .into()
+            } else {
+                Length::zero()
+            },
             current_nesting_level: InlineNestingLevelState {
                 remaining_boxes: InlineBoxChildIter::from_formatting_context(self),
                 fragments_so_far: Vec::with_capacity(self.inline_level_boxes.len()),

components/style/properties/longhands/inherited_text.mako.rs

@@ -65,7 +65,6 @@ ${helpers.predefined_type(
     "LengthPercentage",
     "computed::LengthPercentage::zero()",
     engines="gecko servo-2013 servo-2020",
-    servo_2020_pref="layout.2020.unimplemented",
     animation_value_type="ComputedValue",
     spec="https://drafts.csswg.org/css-text/#propdef-text-indent",
     allow_quirks="Yes",

tests/wpt/metadata-layout-2020/css/CSS2/text/text-indent-rtl-001.xht.ini

@@ -0,0 +1,2 @@
+[text-indent-rtl-001.xht]
+  expected: FAIL

tests/wpt/metadata-layout-2020/css/CSS2/text/text-indent-rtl-002.xht.ini

@@ -0,0 +1,2 @@
+[text-indent-rtl-002.xht]
+  expected: FAIL