WIP: Eliminate event.target() usage from TrayEventFilter

ash/shell_delegate.h

Index: ash/shell_delegate.h
diff --git a/ash/shell_delegate.h b/ash/shell_delegate.h
index 24c92574d6bc77d817cc29e04eb2fb40bc75f46d..468fa62736ab53f0f83da5cfdbaad81d107b199d 100644
--- a/ash/shell_delegate.h
+++ b/ash/shell_delegate.h
@@ -28,17 +28,22 @@ namespace gfx {
 class Image;
 }
 
+namespace keyboard {
+class KeyboardUI;
+}
+
 namespace ui {
 class MenuModel;
 }
 
-namespace keyboard {
-class KeyboardUI;
+namespace views {
+class Widget;
 }
 
 namespace ash {
 
 class AccessibilityDelegate;
+class ContainerDelegate;
 class MediaDelegate;
 class NewWindowDelegate;
 class PointerWatcherDelegate;
@@ -143,6 +148,8 @@ class ASH_EXPORT ShellDelegate {
   virtual std::unique_ptr<PointerWatcherDelegate>
   CreatePointerWatcherDelegate() = 0;
 
+  virtual std::unique_ptr<ContainerDelegate> CreateContainerDelegate() = 0;
+
   // Creates a menu model for the |shelf| and optional shelf |item|.
   // If |item| is null, this creates a context menu for the desktop or shelf.
   virtual ui::MenuModel* CreateContextMenu(ash::Shelf* shelf,