WIP: Eliminate event.target() usage from TrayEventFilter

ash/test/test_shell_delegate.cc

Index: ash/test/test_shell_delegate.cc
diff --git a/ash/test/test_shell_delegate.cc b/ash/test/test_shell_delegate.cc
index 76c76c957d8bbb178668be0052ba150d9564419b..eab081ac8e7c8b5d4f352103ae992ced6d14fe24 100644
--- a/ash/test/test_shell_delegate.cc
+++ b/ash/test/test_shell_delegate.cc
@@ -8,6 +8,7 @@
 
 #include "ash/app_list/app_list_presenter_delegate.h"
 #include "ash/app_list/app_list_presenter_delegate_factory.h"
+#include "ash/container_delegate_aura.h"
 #include "ash/default_accessibility_delegate.h"
 #include "ash/gpu_support_stub.h"
 #include "ash/media_delegate.h"
@@ -205,6 +206,11 @@ MediaDelegate* TestShellDelegate::CreateMediaDelegate() {
   return new MediaDelegateImpl;
 }
 
+std::unique_ptr<ash::ContainerDelegate>
+TestShellDelegate::CreateContainerDelegate() {
+  return base::WrapUnique(new ContainerDelegateAura);
+}
+
 std::unique_ptr<PointerWatcherDelegate>
 TestShellDelegate::CreatePointerWatcherDelegate() {
   return base::WrapUnique(new PointerWatcherDelegateAura);