[WPT] Add automated manual test for InputEvent typing

third_party/WebKit/LayoutTests/external/wpt_automation/input-events/input-events-typing-data-manual-automation.js

+importAutomationScript('/input-events/inputevent_common_input.js');
+
+function inject_input() {
+  return focus('#plain').then(() => {
+    return keyDown('a');
+  }).then(() => {
+    return keyDown('b');
+  }).then(() => {
+    return focus('#rich');
+  }).then(() => {
+    return keyDown('c');
+  }).then(() => {
+    return keyDown('d');
+  });
+}