Fix processing of mouse events on MacViews.

ui/events/cocoa/events_mac.mm

Index: ui/events/cocoa/events_mac.mm
diff --git a/ui/events/cocoa/events_mac.mm b/ui/events/cocoa/events_mac.mm
index 4a8347fd25f67bb93125ef6f5ff82f407334ee13..156fd00bcb196b753ff72bb7160320339d2f82fa 100644
--- a/ui/events/cocoa/events_mac.mm
+++ b/ui/events/cocoa/events_mac.mm
@@ -43,7 +43,7 @@ EventType EventTypeFromNative(const base::NativeEvent& native_event) {
     case NSMouseMoved:
       return ET_MOUSE_MOVED;
     case NSScrollWheel:
-      return ET_SCROLL;
+      return ET_MOUSEWHEEL;

[Avi (use Gerrit), 2016/10/25 15:34:50]

This was recently changed by Trent in r421082; why are you changing this back?

[snake, 2016/10/25 15:46:18]

views::Widget is not supported ET_SCROLL, only ET_MOUSEWHEEL.
see 
https://cs.chromium.org/chromium/src/ui/views/widget/widget.cc?rcl=0&l=1244
Alse see test, added in this CL: NativeWidgetMacTest.MouseWheelEvent
It is failed without this.

[snake, 2016/10/25 20:52:05]

Reverted. 

     case NSMouseEntered:
       return ET_MOUSE_ENTERED;
     case NSMouseExited: