Add generic PaletteDelegate code.

ash/common/wm_shell.h

Index: ash/common/wm_shell.h
diff --git a/ash/common/wm_shell.h b/ash/common/wm_shell.h
index a679e0f2b870add46402bf5b18038f4a1973dc2d..4c2308d929048b0b9848c3c2fa959d491a9d69aa 100644
--- a/ash/common/wm_shell.h
+++ b/ash/common/wm_shell.h
@@ -37,6 +37,7 @@ class KeyboardUI;
 class MaximizeModeController;
 class MruWindowTracker;
 class NewWindowDelegate;
+class PaletteDelegate;
 class ScopedDisableInternalMouseAndKeyboard;
 class SessionStateDelegate;
 class ShelfDelegate;
@@ -117,6 +118,8 @@ class ASH_EXPORT WmShell {
     root_window_for_new_windows_ = root;
   }
 
+  PaletteDelegate* palette_delegate() { return palette_delegate_.get(); }
+
   ShelfDelegate* shelf_delegate() { return shelf_delegate_.get(); }
 
   ShelfModel* shelf_model() { return shelf_model_.get(); }
@@ -347,6 +350,7 @@ class ASH_EXPORT WmShell {
   std::unique_ptr<MediaDelegate> media_delegate_;
   std::unique_ptr<MruWindowTracker> mru_window_tracker_;
   std::unique_ptr<NewWindowDelegate> new_window_delegate_;
+  std::unique_ptr<PaletteDelegate> palette_delegate_;
   std::unique_ptr<ShelfDelegate> shelf_delegate_;
   std::unique_ptr<ShelfModel> shelf_model_;
   std::unique_ptr<ShelfWindowWatcher> shelf_window_watcher_;