Bug 2042924 [wpt PR 60193] - Improve selectedcontent parsing update for select multiple, a=testonly

Automatic update from web-platform-tests
Improve selectedcontent parsing update for select multiple

When a selected option element is done parsing, it triggers an update to
the selectedcontent element of the associated select element. In the
case of a select element with the multiple attribute, this could result
in many clones if multiple options have the selected attribute.

This change improves this by moving the selectedcontent update for
select elements with the multiple attribute from option end tag parsing
to select end tag parsing.

Context: whatwg/html#12430 (comment)

Bug: 483769482
Change-Id: I9ee8a2afe66884da26cbf814b80af7bf430414a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7856275
Reviewed-by: Mason Freed <masonf@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Reviewed-by: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1636613}

--

wpt-commits: 229f4c8b965b0fa27fee7167494173189163502b
wpt-pr: 60193

Author: josepharhar

testing/web-platform/tests/html/semantics/forms/the-select-element/customizable-select/selectedcontent-mutations.html

@@ -402,12 +402,8 @@
     html:
 `<select multiple="" size="1">
     <button>
-      <selectedcontent>
-        <selectedcontent></selectedcontent>
-      </selectedcontent>
-      <selectedcontent>
-        <selectedcontent></selectedcontent>
-      </selectedcontent>
+      <selectedcontent></selectedcontent>
+      <selectedcontent></selectedcontent>
     </button>
     <option>option</option>
   </select>`,
@@ -431,6 +427,8 @@
       "Type: childList | Target: select | Added: [option] | After: #text: \"\"",
       "Type: childList | Target: option | Added: [#text: \"option\"]",
       "Type: childList | Target: select | Added: [#text: \"\"] | After: option",
+      "Type: childList | Target: selectedcontent | Removed: [#text: \"\", selectedcontent, #text: \"\"]",
+      "Type: childList | Target: selectedcontent | Removed: [#text: \"\", selectedcontent, #text: \"\"]",
       "Type: childList | Target: div#test6 | Added: [#text: \"\"] | After: select"
     ]
   },