Use vector icon for Ash shelf launcher

ash/common/shelf/shelf_constants.cc

 // Copyright 2013 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/shelf/shelf_constants.h"
 
 #include "ash/common/material_design/material_design_controller.h"
 #include "base/logging.h"
 
 namespace ash {
 
 const int kInvalidImageResourceID = -1;
 const int kShelfSize = 47;
 const int kShelfButtonSpacing = 10;
 const int kShelfButtonSize = 44;
 const int kTimeToSwitchBackgroundMs = 1000;
 const SkColor kShelfBaseColor = SK_ColorBLACK;
+const SkColor kShelfIconColor = SK_ColorWHITE;
 
 int GetShelfConstant(ShelfConstant shelf_constant) {
   const int kShelfBackgroundAlpha[] = {204, 153, 153};
 
   const int mode = MaterialDesignController::GetMode();
   DCHECK(mode >= MaterialDesignController::NON_MATERIAL &&
          mode <= MaterialDesignController::MATERIAL_EXPERIMENTAL);
 
   switch (shelf_constant) {
     case SHELF_BACKGROUND_ALPHA:
       return kShelfBackgroundAlpha[mode];
   }
   NOTREACHED();
   return 0;
 }
 
 }  // namespace ash