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chromium/third_party/blink/web_tests/http/tests/devtools/oopif/resources/iframe.html 

<body>
    <div>
        <iframe id="iframe-iframe1" src="http://127.0.0.1:8000/devtools/oopif/resources/inner-iframe.html?first"></iframe>
    </div>
    <div>
        <iframe id="iframe-iframe2" src="http://devtools.oopif.test:8000/devtools/oopif/resources/inner-iframe.html?second"></iframe>
    </div>
</body>