WIP: Eliminate event.target() usage from TrayEventFilter

ash/shell/shell_delegate_impl.cc

Index: ash/shell/shell_delegate_impl.cc
diff --git a/ash/shell/shell_delegate_impl.cc b/ash/shell/shell_delegate_impl.cc
index 47f8c52e755af6c9ed5140287bf0940ccf2a97a8..519d2fdfd2a7a26b8c9c09c67b921c80bf5a7b88 100644
--- a/ash/shell/shell_delegate_impl.cc
+++ b/ash/shell/shell_delegate_impl.cc
@@ -6,6 +6,7 @@
 
 #include "ash/accessibility_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/default_user_wallpaper_delegate.h"
 #include "ash/gpu_support_stub.h"
@@ -255,6 +256,11 @@ ash::MediaDelegate* ShellDelegateImpl::CreateMediaDelegate() {
   return new MediaDelegateImpl;
 }
 
+std::unique_ptr<ash::ContainerDelegate>
+ShellDelegateImpl::CreateContainerDelegate() {
+  return base::WrapUnique(new ContainerDelegateAura);
+}
+
 std::unique_ptr<ash::PointerWatcherDelegate>
 ShellDelegateImpl::CreatePointerWatcherDelegate() {
   return base::WrapUnique(new PointerWatcherDelegateAura);