ui: Cleanup class/struct forward declarations

chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h

Index: chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h
diff --git a/chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h b/chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h
index 08320488d7af7adc877a2e9e0b471afd3e871f3c..1ed0e117e3df70489d94095650b478fb205dad89 100644
--- a/chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h
+++ b/chrome/browser/ui/views/javascript_app_modal_event_blocker_x11.h
@@ -14,6 +14,10 @@ namespace aura {
 class Window;
 }
 
+namespace ui {
+class EventTarget;
+}
+
 // JavascriptAppModalEventBlockerX11 blocks events to all browser windows except
 // the browser window which hosts |app_modal_window| for the duration of its
 // lifetime. JavascriptAppModalEventBlockerX11 should not outlive