Mac: Share kScrollbarPixelsPerCocoaTick between ui:: and blink:: events

ui/events/cocoa/cocoa_event_utils.h

 // 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.
 
 #ifndef UI_EVENTS_COCOA_COCOA_EVENT_UTILS_H_
 #define UI_EVENTS_COCOA_COCOA_EVENT_UTILS_H_
 
 #import <Cocoa/Cocoa.h>
 
 #include "ui/events/events_export.h"
 
 namespace ui {
 
+// Conversion between wheel delta amounts and number of pixels to scroll.
+constexpr double kScrollbarPixelsPerCocoaTick = 40.0;

[Avi (use Gerrit), 2016/08/10 15:17:29]

Is that the new preferred style? I thought enum or exported constant was the
style.

[tapted, 2016/08/11 01:24:08]

http://go/cppguide#Use_of_constexpr is pretty much "constexpr whenever you can"
(also, e.g, http://go/cppguide#Static_and_Global_Variables ). E.g. it prevents
the compiler slipping in a static initializer you don't want. Exporting is
somewhat orthogonal -- it's still required if something takes the address --
constexpr doesn't prevent that but `enum` would. However, I avoided enum since I
would have to change it to an integral constant (which I guess it could be...
but wasn't before).

+
 // Converts the Cocoa |modifiers| bitsum into a ui::EventFlags bitsum.
 EVENTS_EXPORT int EventFlagsFromModifiers(NSUInteger modifiers);
 
 // Retrieves a bitsum of ui::EventFlags represented by |event|,
 // but instead use the modifier flags given by |modifiers|,
 // which is the same format as |-NSEvent modifierFlags|. This allows
 // substitution of the modifiers without having to create a new event from
 // scratch.
 EVENTS_EXPORT int EventFlagsFromNSEventWithModifiers(NSEvent* event,
                                                      NSUInteger modifiers);
 }  // namespace ui
 
 #endif  // UI_EVENTS_COCOA_COCOA_EVENT_UTILS_H_