WIP: Eliminate event.target() usage from TrayEventFilter

content/renderer/mus/compositor_mus_connection.cc

Index: content/renderer/mus/compositor_mus_connection.cc
diff --git a/content/renderer/mus/compositor_mus_connection.cc b/content/renderer/mus/compositor_mus_connection.cc
index 8569d1836e93f3d1c99584d5a582e9b3fdc8103b..cf7406cb9c89152facca455543565b90d92b98fd 100644
--- a/content/renderer/mus/compositor_mus_connection.cc
+++ b/content/renderer/mus/compositor_mus_connection.cc
@@ -116,7 +116,8 @@ void CompositorMusConnection::OnEmbed(mus::Window* root) {
   }
 }
 
-void CompositorMusConnection::OnEventObserved(const ui::Event& event) {
+void CompositorMusConnection::OnEventObserved(const ui::Event& event,
+                                              mus::Window* target) {
   // Compositor does not use SetEventObserver().
 }