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,

[sadrul, 2015/09/09 04:19:04]

Do we need 'wheel' as a separate kind? e.g. both mouse and pen can send wheel
events I think?

[rjkroege, 2015/09/09 19:45:38]

Based on http://www.w3.org/TR/pointerevents/#pointerevent-interface and the DOM
level 3 spec, I think that it's reasonable to make them separate. But I may have
(mis)read the wrong specs.

[sadrul, 2015/09/10 17:39:15]

I am not sure. I feel like the event-type should be sufficient here, and the
PointerKind would be more useful as an indication of what kind of device it
originated from (so it could be used to treat events coming from a normal mouse
differently than events coming from a touchpad). If we use WHEEL for both of
these kinds of events, we would lose that information.

[rjkroege, 2015/09/12 01:29:02]

I agree. In Web spec land, Pointer encompasses touch, pen, mouse. while Wheel is
completely separate.

I made wheel a new kind of top-level event distinct from Pointer. 

 };
+
+enum WheelMode {
+  PIXEL,
+  LINE,
+  PAGE,
+  SCALING,
+};