Auto merge of #21976 - notriddle:iframe-target-form-race, r=jdm

Assign a name to iframes when loading the initial about:blank

Before, it would assign the name too late, causing scripts (which will not wait for another tick) to accidentally spawn pop-up windows instead of loading into the iframe.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #21886
- [x] There are tests for these changes

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tests/wpt/metadata/MANIFEST.json

@@ -293185,6 +293185,11 @@
      {}
     ]
    ],
+   "html/semantics/forms/form-submission-target/form-target-iframe-helper.py": [
+    [
+     {}
+    ]
+   ],
    "html/semantics/forms/introduction-1/contains.json": [
     [
      {}
@@ -368139,6 +368144,12 @@
      {}
     ]
    ],
+   "html/semantics/forms/form-submission-target/form-target-iframe.html": [
+    [
+     "/html/semantics/forms/form-submission-target/form-target-iframe.html",
+     {}
+    ]
+   ],
    "html/semantics/forms/historical.html": [
     [
      "/html/semantics/forms/historical.html",
@@ -617924,6 +617935,14 @@
    "d05364387e62dfedc857628af833c3558ee3d1db",
    "testharness"
   ],
+  "html/semantics/forms/form-submission-target/form-target-iframe-helper.py": [
+   "291221a9f6ba8876a022021c53c38ff28a3fd893",
+   "support"
+  ],
+  "html/semantics/forms/form-submission-target/form-target-iframe.html": [
+   "f37bc33f6f93ca94940ffeb0066945eb9aa020ee",
+   "testharness"
+  ],
   "html/semantics/forms/historical.html": [
    "6873ecd251741fb8436a377081d5a6d3de53b7ab",
    "testharness"

tests/wpt/metadata/html/browsers/windows/targeting-cross-origin-nested-browsing-contexts.html.ini

@@ -1,4 +1,5 @@
 [targeting-cross-origin-nested-browsing-contexts.html]
   type: testharness
+  disabled: https://github.com/servo/servo/issues/10056
   [Targeting nested browsing contexts]
     expected: FAIL