Don't trim leading whitespace of anonymous table cells (#31803)

A sequence of whitespace shouldn't generate an anonymous table row/cell,
but we can't just throw away the leading whitespace, because afterwards
we may encounter some other content, and then the leading whitespace
should appear in the cell (noticeable with e.g. `white-space: pre`).

components/layout_2020/table/construct.rs

@@ -56,6 +56,19 @@ pub(crate) enum AnonymousTableContent<'dom, Node> {
     },
 }
 
+impl<'dom, Node> AnonymousTableContent<'dom, Node> {
+    fn is_whitespace_only(&self) -> bool {
+        match self {
+            Self::Element { .. } => false,
+            Self::Text(_, ref text) => text.chars().all(char_is_whitespace),
+        }
+    }
+
+    fn contents_are_whitespace_only(contents: &[Self]) -> bool {
+        contents.iter().all(|content| content.is_whitespace_only())
+    }
+}
+
 impl Table {
     pub(crate) fn construct<'dom>(
         context: &LayoutContext,
@@ -627,7 +640,9 @@ where
     }
 
     fn finish_anonymous_row_if_needed(&mut self) {
-        if self.current_anonymous_row_content.is_empty() {
+        if AnonymousTableContent::contents_are_whitespace_only(&self.current_anonymous_row_content)
+        {
+            self.current_anonymous_row_content.clear();
             return;
         }
 
@@ -689,9 +704,6 @@ where
     Node: NodeExt<'dom>,
 {
     fn handle_text(&mut self, info: &NodeAndStyleInfo<Node>, text: Cow<'dom, str>) {
-        if text.chars().all(char_is_whitespace) {
-            return;
-        }
         self.current_anonymous_row_content
             .push(AnonymousTableContent::Text(info.clone(), text));
     }
@@ -897,7 +909,9 @@ where
     }
 
     fn finish_current_anonymous_cell_if_needed(&mut self) {
-        if self.current_anonymous_cell_content.is_empty() {
+        if AnonymousTableContent::contents_are_whitespace_only(&self.current_anonymous_cell_content)
+        {
+            self.current_anonymous_cell_content.clear();
             return;
         }
 
@@ -947,9 +961,6 @@ where
     Node: NodeExt<'dom>,
 {
     fn handle_text(&mut self, info: &NodeAndStyleInfo<Node>, text: Cow<'dom, str>) {
-        if text.chars().all(char_is_whitespace) {
-            return;
-        }
         self.current_anonymous_cell_content
             .push(AnonymousTableContent::Text(info.clone(), text));
     }

tests/wpt/meta/css/css-tables/table-model-fixup.html.ini

@@ -14,8 +14,5 @@
   [2.2. An anonymous table-row box must be generated around each sequence of consecutive children of a table-row-grouping box which are not table-row boxes. (3/3)]
     expected: FAIL
 
-  [1.4. Anonymous inline boxes which contains only white space and are between two immediate siblings *each* of which is a table-non-root element, are treated as if they had display: none.]
-    expected: FAIL
-
   [2.3 happens after 2.1. and 2.2. (1/2)]
     expected: FAIL