Fix dir=auto traversal exclusions to apply to assigned nodes in a slot.

This fixes Chromium code and web platform tests to match half of the
spec update in whatwg/html#10488 and
whatwg/html#10561 .  Prior to this change (in
both spec and Chromium implementation) subtrees that were intended to be
excluded from dir=auto traversal were not being excluded if they were an
assigned node in a slot with dir=auto (which has a special traversal to
traverse in the order of the assigned nodes, despite the general
traversal being on the dom tree and not the flat tree).

This fix is behind the DirAutoFixSlotExclusions flag in case we need to
disable it.

This also updates the test for bdi elements to only check for bdi
elements in the HTML namespace.

Bug: 576815, 352191350
Change-Id: I58a3bef05d27ba83a7e6b8e34d7bba74a8e0a482
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5796604
Reviewed-by: Di Zhang <dizhangg@chromium.org>
Commit-Queue: David Baron <dbaron@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1343841}

html/dom/elements/global-attributes/dir-auto-dynamic-changes.window.js

@@ -371,12 +371,9 @@ test(() => {
     <slot dir=auto></slot>
   `);
   let slot = shadow.querySelector("slot");
-  assert_equals(html_direction(slot), "rtl");
-  let inp = tree.querySelector("input");
-  inp.value = "abc";
   assert_equals(html_direction(slot), "ltr");
   tree.remove();
-}, 'dir=auto slot is updated by text in value of input element children');
+}, 'dir=auto slot is not affected by text in value of input element children');
 
 test(() => {
   let [tree, shadow] = setup_tree(`

html/dom/elements/global-attributes/dir-slots-directionality.html

@@ -173,9 +173,9 @@
   let div = tree.querySelector("#root");
   assert_equals(html_direction(div), "ltr");
   let slot = shadow.querySelector("slot");
-  assert_equals(html_direction(slot), "rtl");
+  assert_equals(html_direction(slot), "ltr");
   tree.remove();
-}, 'dir=auto slot ignores dir attribute of assigned nodes');
+}, 'dir=auto slot ignores assigned nodes with dir attribute');
 
 test(() => {
   let [tree, shadow] = setup_tree(`
@@ -188,9 +188,9 @@
     <slot dir="auto"></slot>
   `);
   let slot = shadow.querySelector("slot");
-  assert_equals(html_direction(slot), "rtl");
+  assert_equals(html_direction(slot), "ltr");
   tree.remove();
-}, 'dir=auto slot considers text in bdi assigned nodes');
+}, 'dir=auto slot ignores text in bdi assigned nodes');
 
 test(() => {
   let [tree, shadow] = setup_tree(`
@@ -205,13 +205,13 @@
   let inp = tree.querySelector("input");
   assert_equals(html_direction(inp), "ltr");
   let slot = shadow.querySelector("slot");
-  assert_equals(html_direction(slot), "rtl");
+  assert_equals(html_direction(slot), "ltr");
   tree.remove();
 
   [tree, shadow] = setup_tree(`
     <div>
       <div id=root>
-        <input value=" ">
+        <input value="a">
         اختبر
       </div>
     </div>
@@ -221,8 +221,8 @@
   inp = tree.querySelector("input");
   assert_equals(html_direction(inp), "ltr");
   slot = shadow.querySelector("slot");
-  assert_equals(html_direction(slot), "ltr", "no strong character in value counts as ltr");
+  assert_equals(html_direction(slot), "rtl");
   tree.remove();
-}, 'dir=auto slot considers text in value of input element children');
+}, 'dir=auto slot ignores text in value of input element children');
 
 </script>