Auto merge of #22769 - gterzian:use_thread_pool_in_resource_thread, r=nox

Use a threadpool for fetch

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #22768 (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because ___

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -13052,6 +13052,19 @@
      {}
     ]
    ],
+   "mozilla/fetch_cannot_overwhelm_system.window.js": [
+    [
+     "mozilla/fetch_cannot_overwhelm_system.window.html",
+     {
+      "script_metadata": [
+       [
+        "title",
+        "Ensure multiple fetch do not crash the browser."
+       ]
+      ]
+     }
+    ]
+   ],
    "mozilla/first-reflow-sheet-assert.html": [
     [
      "mozilla/first-reflow-sheet-assert.html",
@@ -20057,6 +20070,10 @@
    "0ba1ce0d5577de68e5e8ff3acbce52043e7dee43",
    "testharness"
   ],
+  "mozilla/fetch_cannot_overwhelm_system.window.js": [
+   "989231e9caedd099f5212bd2f9d377c83f929a22",
+   "testharness"
+  ],
   "mozilla/first-reflow-sheet-assert.html": [
    "268af6d333f04adc35974ca3f2e9ebb29783fd2e",
    "testharness"

tests/wpt/mozilla/meta/mozilla/fetch_cannot_overwhelm_system.window.js.ini

@@ -0,0 +1,3 @@
+[fetch_cannot_overwhelm_system.window.html]
+  expected:
+      if os == "linux": CRASH

tests/wpt/mozilla/tests/mozilla/fetch_cannot_overwhelm_system.window.js

@@ -0,0 +1,15 @@
+// META: title=Ensure multiple fetch do not crash the browser.
+
+async_test(function(t) {
+  onload = t.step_func(function() {
+    var step;
+    var xhr
+    var url = '/';
+    t.step_timeout(t.step_func_done(), 10);
+    for (step = 0; step < 5000; step++) {
+      xhr = new XMLHttpRequest();
+      xhr.open('GET', url, true);
+      xhr.send();
+    }
+  });
+});