Fix processing of mouse events on MacViews.

ui/views/test/event_generator_delegate_mac.mm

Index: ui/views/test/event_generator_delegate_mac.mm
diff --git a/ui/views/test/event_generator_delegate_mac.mm b/ui/views/test/event_generator_delegate_mac.mm
index 55005ea2c4647103ab53c465a2105e3f0cd20934..d96246a90e1ce9c7b82678ed5856ea75520c2f64 100644
--- a/ui/views/test/event_generator_delegate_mac.mm
+++ b/ui/views/test/event_generator_delegate_mac.mm
@@ -172,12 +172,10 @@ void EmulateSendEvent(NSWindow* window, NSEvent* event) {
       [responder scrollWheel:event];
       break;
     case NSMouseEntered:
+      [responder mouseEntered:event];
+      break;
     case NSMouseExited:
-      // With the assumptions in NSMouseMoved, it doesn't make sense for the
-      // generator to handle entered/exited separately. It's the responsibility
-      // of views::internal::RootView to convert the moved events into entered
-      // and exited events for the individual views.
-      NOTREACHED();
+      [responder mouseExited:event];
       break;
     case NSEventTypeSwipe:
       // NSEventTypeSwipe events can't be generated using public interfaces on
@@ -206,15 +204,38 @@ void EmulateSendEvent(NSWindow* window, NSEvent* event) {
   NSPoint point = ConvertRootPointToTarget(window, point_in_root);
   NSUInteger modifiers = 0;
   NSEventType type = EventTypeToNative(event_type, flags, &modifiers);
-  return [NSEvent mouseEventWithType:type
-                            location:point
-                       modifierFlags:modifiers
-                           timestamp:0
-                        windowNumber:[window windowNumber]
-                             context:nil
-                         eventNumber:0
-                          clickCount:click_count
-                            pressure:1.0];
+  if (type == NSMouseEntered || type == NSMouseExited) {
+    return [NSEvent enterExitEventWithType:type
+                                  location:point
+                             modifierFlags:modifiers
+                                 timestamp:0
+                              windowNumber:[window windowNumber]
+                                   context:nil
+                               eventNumber:0
+                            trackingNumber:0
+                                  userData:nil];
+  } else {
+    return [NSEvent mouseEventWithType:type
+                              location:point
+                         modifierFlags:modifiers
+                             timestamp:0
+                          windowNumber:[window windowNumber]
+                               context:nil
+                           eventNumber:0
+                            clickCount:click_count
+                              pressure:1.0];
+  }
+}
+
+NSEvent* CreateMouseWheelEventInWindow(NSWindow* window,
+                                       ui::MouseEvent* mouse_event) {
+  DCHECK(mouse_event->type() == ui::ET_MOUSEWHEEL);
+  ui::MouseWheelEvent* mouse_wheel_event =
+      static_cast<ui::MouseWheelEvent*>(mouse_event);
+  return cocoa_test_event_utils::TestScrollEvent(
+      ConvertRootPointToTarget(window, mouse_wheel_event->location()), window,
+      mouse_wheel_event->x_offset(), mouse_wheel_event->y_offset(), false,
+      NSEventPhaseNone, NSEventPhaseNone);
 }
 
 // Implementation of ui::test::EventGeneratorDelegate for Mac. Everything
@@ -349,10 +370,12 @@ void DispatchKeyEventToIME(EventTarget* target,
 }
 
 void EventGeneratorDelegateMac::OnMouseEvent(ui::MouseEvent* event) {
-  NSEvent* ns_event = CreateMouseEventInWindow(window_,
-                                               event->type(),
-                                               event->location(),
-                                               event->changed_button_flags());
+  NSEvent* ns_event =
+      event->type() == ui::ET_MOUSEWHEEL
+          ? CreateMouseWheelEventInWindow(window_, event)
+          : CreateMouseEventInWindow(window_, event->type(), event->location(),
+                                     event->changed_button_flags());
+
   if (owner_->targeting_application())
     [NSApp sendEvent:ns_event];
   else