[WPT] Add automated manual test for InputEvent typing

third_party/WebKit/LayoutTests/external/wpt_automation/input-events/inputevent_common_input.js

+// Returns a Promise for future conversion into WebDriver-backed API.
+function keyDown(key, modifiers) {
+  return new Promise(function(resolve, reject) {
+    if (window.eventSender) {
+      eventSender.keyDown(key, modifiers);
+      resolve();
+    } else {
+      reject();
+    }
+  });
+}
+
+function focusAndKeyDown(selector, key, modifiers) {
+  document.querySelector(selector).focus();
+  return keyDown(key, modifiers);
+}
+
+{
+  const inputevent_automation = async_test("InputEvent Automation");
+  // Defined in every test and should return a promise that gets resolved when input is finished.
+  inject_input().then(inputevent_automation.step_func_done());
+}