Overhaul Mandoline event transport code

ui/mojo/events/input_event_constants.mojom

 // Copyright 2014 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.
 
 module mojo;
 
 enum EventType {
   UNKNOWN,
   KEY_PRESSED,
   KEY_RELEASED,
@@ skipping 23 matching lines @@
 
 enum MouseEventFlags {
   IS_DOUBLE_CLICK     =  65536,
   IS_TRIPLE_CLICK     = 131072,
   IS_NON_CLIENT       = 262144,
 
   // TODO(erg): Move accessibility flags and maybe synthetic touch events here.
 };
 
 enum PointerKind {
+  UNKNOWN,
+  MOUSE,
+  PEN,
   TOUCH,
-  MOUSE,
+  WHEEL,
 };
+
+enum WheelMode {
+  PIXEL,
+  LINE,
+  PAGE,
+  SCALING,
+};