Verify that shadow roots with identical styles share style resolvers (have equal identifier below).
<input></input>
<textarea></textarea>
<div id=a></div>
<div id=b></div>
<div id=c></div>
<div id=d></div>
<div id=e></div>
<div id=f></div>
<div id=g></div>
<div id=h></div>
<div id=i></div>

<pre id=log></pre>

<script>
if (window.testRunner)
    testRunner.dumpAsText();

function attachShadowWithStyle(id, style)
{
    const element = document.querySelector("#" + id);
    const shadow = element.attachShadow({ mode: "open" });
    shadow.innerHTML = `
        <style>${ style }</style>
        <div>${ id }</div>
    `;
}

attachShadowWithStyle("a", "");
attachShadowWithStyle("b", "");
attachShadowWithStyle("c", "");
attachShadowWithStyle("d", "");
attachShadowWithStyle("e", "div { color: green }");
attachShadowWithStyle("f", "div { color: green }");
attachShadowWithStyle("g", "div { color: green }");
attachShadowWithStyle("h", "div { color: green }");
attachShadowWithStyle("i", "div { color: green }");

if (window.internals) {
    log.textContent += internals.dumpStyleResolvers();
    log.textContent += "\nAfter style mutation\n"
}

c.shadowRoot.querySelector("style").textContent = "div { color: green }";

{
    const styleElement = document.createElement("style");
    styleElement.textContent = "div { color: green }";
    d.shadowRoot.appendChild(styleElement);
}
{
    const styleElement = document.createElement("style");
    styleElement.textContent = "div { color: blue }";
    e.shadowRoot.appendChild(styleElement);
}

f.shadowRoot.querySelector("style").sheet.addRule("div", "color: blue");
g.shadowRoot.querySelector("style").textContent = "";
h.shadowRoot.querySelector("style").remove();

if (window.internals)
    log.textContent += internals.dumpStyleResolvers();

</script>