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

ui/views/corewm/focus_controller.cc

Index: ui/views/corewm/focus_controller.cc
diff --git a/ui/views/corewm/focus_controller.cc b/ui/views/corewm/focus_controller.cc
index b5bbd90b588b498ff234f167bf09ed6da5f81444..f095bbe27b64bb3f8d9b73cb83b66bb48d5e1745 100644
--- a/ui/views/corewm/focus_controller.cc
+++ b/ui/views/corewm/focus_controller.cc
@@ -152,10 +152,9 @@ void FocusController::OnWindowHiddenInRootWindow(
 void FocusController::OnKeyEvent(ui::KeyEvent* event) {
 }
 
-ui::EventResult FocusController::OnMouseEvent(ui::MouseEvent* event) {
+void FocusController::OnMouseEvent(ui::MouseEvent* event) {
   if (event->type() == ui::ET_MOUSE_PRESSED)
     WindowFocusedFromInputEvent(static_cast<aura::Window*>(event->target()));
-  return ui::ER_UNHANDLED;
 }
 
 void FocusController::OnScrollEvent(ui::ScrollEvent* event) {