Don't require a LayoutObject when 'src' changes on an embed

[chromium-wpt-export-bot]

When an embed element has no 'src' and no 'type', it represents
nothing. When the 'src' would be changed to non-empty in that state
there would be no LayoutObject, and thus attach was not triggered
for the element.

By-pass the check for a LayoutObject in this case.

Guarded by the "HTMLEmbedElementRepresentsNothingToActive" flag.

Fixed: 479233864
Change-Id: If5bf5cc2684e146dfc56dda02f12e930a134a717
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7524670
Commit-Queue: Fredrik Söderquist <[email protected]>
Reviewed-by: Morten Stenshorne <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1576496}

[community-tc-integration]

Uh oh! Looks like an error!

Client ID static/taskcluster/github does not have sufficient scopes and is missing the following scopes:

{
  "AnyOf": [
    "queue:rerun-task:taskcluster-github/RrfqqFHXRxyRLTHT-jus8w/RrfqqFHXRxyRLTHT-jus8w",
    "queue:rerun-task-in-project:none",
    {
      "AllOf": [
        "queue:rerun-task",
        "assume:scheduler-id:taskcluster-github/RrfqqFHXRxyRLTHT-jus8w"
      ]
    }
  ]
}

This request requires the client to satisfy the following scope expression:

{
  "AnyOf": [
    "queue:rerun-task:taskcluster-github/RrfqqFHXRxyRLTHT-jus8w/RrfqqFHXRxyRLTHT-jus8w",
    "queue:rerun-task-in-project:none",
    {
      "AllOf": [
        "queue:rerun-task",
        "assume:scheduler-id:taskcluster-github/RrfqqFHXRxyRLTHT-jus8w"
      ]
    }
  ]
}

---

• method: rerunTask
• errorCode: InsufficientScopes
• statusCode: 403
• time: 2026-01-29T12:46:23.010Z

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.

[jonathan-j-lee]

The <embed> in the PR description causes wpt-decision-task to fail: #53933