Add pref to enable/disable palette tray.

ash/common/system/chromeos/palette/palette_tray.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_BUTTON_TRAY_H_
 #define ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_BUTTON_TRAY_H_
 
 #include <map>
 #include <memory>
 
 #include "ash/ash_export.h"
+#include "ash/common/palette_delegate.h"
 #include "ash/common/session/session_state_observer.h"
 #include "ash/common/shell_observer.h"
 #include "ash/common/system/chromeos/palette/palette_tool_manager.h"
 #include "ash/common/system/tray/tray_background_view.h"
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 
 namespace views {
 class ImageView;
 class Widget;
 }
 
 namespace ash {
 
 class TrayBubbleWrapper;
 class PaletteToolManager;
@@ skipping 48 matching lines @@
   // Creates a new border for the icon. The padding is determined based on the
   // alignment of the shelf.
   void SetIconBorderForShelfAlignment();
 
   // Updates the tray icon from the palette tool manager.
   void UpdateTrayIcon();
 
   // Sets the icon to visible if the palette can be used.
   void UpdateIconVisibility();
 
+  // Called when the palette enabled pref has changed.
+  void OnPaletteEnabledPrefChanged(bool enabled);
+
   bool OpenBubble();
   void AddToolsToView(views::View* host);
 
   std::unique_ptr<PaletteToolManager> palette_tool_manager_;
   std::unique_ptr<TrayBubbleWrapper> bubble_;
 
+  // Manages the callback OnPaletteEnabledPrefChanged callback registered to
+  // the PaletteDelegate instance.
+  std::unique_ptr<PaletteDelegate::EnableListenerSubscription> palette_enabled_;

[stevenjb, 2016/08/23 17:36:41]

This is a confusing variable name, I would use palette_enabled_subscription_ or
somesuch.

[jdufault, 2016/08/23 22:49:56]

Done.

+
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;
 
+  base::WeakPtrFactory<PaletteTray> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(PaletteTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_CHROMEOS_PALETTE_PALETTE_BUTTON_TRAY_H_