[WPT] Add automated manual test for InputEvent typing

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

+function keyDown(key, modifiers) {
+  return new Promise(function(resolve, reject) {
+    if (window.eventSender) {
+      eventSender.keyDown(key, modifiers);
+      resolve();
+    } else {
+      reject();
+    }
+  });
+}
+
+function focus(selector) {
+  return new Promise(function(resolve, reject) {
+    document.querySelector(selector).focus();

[foolip, 2017/06/01 13:54:21]

Can you add a comment about why both this and keyDown are wrapped as promises
even though they could be synchronous? For keyDown I suspect the answer is the
ability to convert into a WebDriver-backed API, but for focus() I don't know,
that doesn't require any special powers.

[chongz, 2017/06/01 15:34:13]

Yes I was thinking if we are going to use WebDriver-backed API for keyDown(),
but you are right we don't need special power for focus().

Added comment and changed |focus() => focusAndKeyDown()|.

+    resolve();
+  });
+}
+
+{
+  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(function() {
+    inputevent_automation.done();

[foolip, 2017/06/01 13:54:21]

optional nit: could make this
inject_input().then(inputevent_automation.step_func_done());

[chongz, 2017/06/01 15:34:13]

Done.

+  });
+}