events: Update mouse-event handlers to not return EventResult.

ash/system/tray/tray_event_filter.cc

Index: ash/system/tray/tray_event_filter.cc
diff --git a/ash/system/tray/tray_event_filter.cc b/ash/system/tray/tray_event_filter.cc
index e1a223c1cf6629352947815b481060af838ef789..dfba4fe17f53f5fd9e93eed0d0f069384439c404 100644
--- a/ash/system/tray/tray_event_filter.cc
+++ b/ash/system/tray/tray_event_filter.cc
@@ -28,12 +28,11 @@ TrayEventFilter::~TrayEventFilter() {
   ash::Shell::GetInstance()->RemovePreTargetHandler(this);
 }
 
-ui::EventResult TrayEventFilter::OnMouseEvent(ui::MouseEvent* event) {
+void TrayEventFilter::OnMouseEvent(ui::MouseEvent* event) {
   if (event->type() == ui::ET_MOUSE_PRESSED &&
       ProcessLocatedEvent(event)) {
-    return ui::ER_CONSUMED;
+    event->StopPropagation();
   }
-  return ui::ER_UNHANDLED;
 }
 
 void TrayEventFilter::OnTouchEvent(ui::TouchEvent* event) {