[DevTools] Migrate inspector-protocol/emulation tests to new harness

third_party/WebKit/LayoutTests/inspector-protocol/emulation/device-emulation-small-dw.js

+(async function(testRunner) {
+  let {page, session, dp} = await testRunner.startBlank(`
+    Tests that device emulation affects media rules, viewport meta tag, body dimensions and window.screen.
+    Emulating small device on a page with viewport "width=device-width" set should work without reload for page without scrollbar.
+  `);
+
+  var DeviceEmulator = await testRunner.loadScript('../resources/device-emulator.js');
+  var deviceEmulator = new DeviceEmulator(testRunner, session);
+  await deviceEmulator.emulate(380, 420, 1);
+
+  var viewport = 'w=dw';
+  testRunner.log(`Loading page with viewport=${viewport}`);
+  await session.navigate('../resources/device-emulation.html?' + viewport);
+  await session.evaluate(`document.body.classList.add('small')`);
+
+  testRunner.log(await session.evaluate(`dumpMetrics(true)`));
+  testRunner.completeTest();
+})