Fix the wrong styte of waiting EventWatcher's promise

EventWatcher promise was waited with mixed style. Code was fixed to use
only one style of waiting. After change EventWatcher eventTypes
parameter value needed to change also to able to run test correctly.

device-posture/device-posture.https.html

@@ -19,13 +19,12 @@
 
 // REFERENCE https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/http/tests/inspector-protocol/device-posture/device-posture-change-event.js
 device_posture_test(async (t) => {
-  const watcher = new EventWatcher(t, navigator.devicePosture, ['change']);
+  const watcher = new EventWatcher(t, navigator.devicePosture, ['onchange']);
   const postures = ['folded', 'continuous', 'folded'];
   for (const posture of postures) {
     await test_driver.set_device_posture(posture);
-    await watcher.wait_for('change').then(() => {
-      assert_equals(posture, navigator.devicePosture.type);
-    });
+    await watcher;
+    assert_equals(posture, navigator.devicePosture.type);
   }
 }, 'Device posture test: device-posture-change-event.js.');