Add common palette tray implementation.

ash/common/system/chromeos/palette/palette_tool.cc

 // 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.
 
 #include "ash/common/system/chromeos/palette/palette_tool.h"
 
-#include "base/logging.h"
+#include "ash/common/system/chromeos/palette/palette_tool_manager.h"
 
 namespace ash {
 
 // static
 void PaletteTool::RegisterToolInstances(PaletteToolManager* tool_manager) {}
 
 PaletteTool::PaletteTool(Delegate* delegate) : delegate_(delegate) {}
 
 PaletteTool::~PaletteTool() {}
 
 void PaletteTool::OnEnable() {
   enabled_ = true;
 }
 
 void PaletteTool::OnDisable() {
   enabled_ = false;
 }
 
 base::Optional<gfx::VectorIconId> PaletteTool::GetActiveTrayIcon() {
   return base::Optional<gfx::VectorIconId>();
 }
 
 }  // namespace ash