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,
   POINTER_CANCEL,
   POINTER_DOWN,
   POINTER_MOVE,
   POINTER_UP,
+  WHEEL,
 };
 
 // This mirrors ui::EventFlags
 // TODO(morrita): Use shift operator once it is available.
 enum EventFlags {
   NONE                =      0,
   CAPS_LOCK_DOWN      =      1,
   SHIFT_DOWN          =      2,
   CONTROL_DOWN        =      4,
   ALT_DOWN            =      8,
   LEFT_MOUSE_BUTTON   =     16,
   MIDDLE_MOUSE_BUTTON =     32,
   RIGHT_MOUSE_BUTTON  =     64,
   COMMAND_DOWN        =    128,
   EXTENDED            =    256,
   IS_SYNTHESIZED      =    512,
   ALTGR_DOWN          =   1024,
   MOD3_DOWN           =   2048
 };
 
 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 {
+  MOUSE,
+  PEN,
   TOUCH,
-  MOUSE,
 };
+
+enum WheelMode {
+  PIXEL,
+  LINE,
+  PAGE,
+  SCALING,
+};