[DevTools] New harness for inspector-protocol layout tests

third_party/WebKit/LayoutTests/inspector-protocol/page/frameStartedLoading.js

+(async function() {
+  let {page, session, Protocol} = await InspectorTest.startBlank('');
+
+  Protocol.Page.enable();
+  session.evaluate(`
+    var frame = document.createElement('iframe');
+    frame.src = '${InspectorTest.url('../resources/blank.html')}';
+    document.body.appendChild(frame);
+  `);
+  await Protocol.Page.onceFrameStartedLoading();
+  InspectorTest.log('Started loading');
+  await Protocol.Page.onceFrameStoppedLoading();
+  InspectorTest.log('Stopped loading');
+  InspectorTest.completeTest();
+})();