[InputEvent] Add InputEvent with basic interface behind a flag

third_party/WebKit/Source/core/events/InputEventInit.idl

Index: third_party/WebKit/Source/core/events/InputEventInit.idl
diff --git a/third_party/WebKit/Source/core/events/InputEventInit.idl b/third_party/WebKit/Source/core/events/InputEventInit.idl
new file mode 100644
index 0000000000000000000000000000000000000000..6b2d07dc84c49e4e5a2ca9d2c2711cd71feefb9c
--- /dev/null
+++ b/third_party/WebKit/Source/core/events/InputEventInit.idl
@@ -0,0 +1,11 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// https://w3c.github.io/editing/input-events.html
+
+[
+    RuntimeEnabled=InputEvent,
+] dictionary InputEventInit : UIEventInit {
+    // TODO(chongz): Add 'inputType', 'data', 'isComposing' and 'targetRanges'
+};