[DevTools] New harness for inspector-protocol layout tests

third_party/WebKit/LayoutTests/inspector-protocol/shadow-dom-rules-in-styleSheetAddedEvent.js

+(async function(testRunner) {
+  let {page, session, dp} = await testRunner.startHTML(`
+    <div id='host'></div>
+    <template id='tmpl'>
+      <style> .red { color: red; } </style>
+      <div id='inner' class='red'>hi!</div>
+    </template>
+  `, 'This test checks that style sheets hosted inside shadow roots are reported in CSS.styleSheetAdded event.');
+
+  await session.evaluate(`
+    var template = document.querySelector('#tmpl');
+    var root = document.querySelector('#host').createShadowRoot();
+    root.appendChild(template.content.cloneNode(true));
+  `);
+
+  dp.DOM.enable();
+  dp.CSS.enable();
+  var msg = await dp.CSS.onceStyleSheetAdded();
+  var styleSheetHeader = msg.params.header;
+  var payload = await dp.CSS.getStyleSheetText({styleSheetId: styleSheetHeader.styleSheetId});
+  testRunner.log('Loaded style sheet text: ' + payload.result.text);
+  testRunner.completeTest();
+})