Use browser top chrome material design by default on Chrome OS

ui/base/material_design/material_design_controller.h

 // Copyright 2015 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 UI_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_
 #define UI_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "ui/base/ui_base_export.h"
 
@@ skipping 16 matching lines @@
     // Material design targeted at mouse/touch hybrid devices.
     MATERIAL_HYBRID = 2
   };
 
   // Get the current Mode that should be used by the system.
   static Mode GetMode();
 
   // Returns true if the current mode is a material design variant.
   static bool IsModeMaterial();
 
+  // Returns the per-platform default material design variant.
+  static Mode DefaultMode();
+
  private:
   friend class test::MaterialDesignControllerTestAPI;
 
   // Tracks whether |mode_| has been initialized. This is necessary so tests can
   // reset the state back to a clean state during tear down.
   static bool is_mode_initialized_;
 
   // The current Mode to be used by the system.
   static Mode mode_;
 
@@ skipping 11 matching lines @@
   // Set |mode_| to |mode| and updates |is_mode_initialized_| to true. Can be
   // used by tests to directly set the mode.
   static void SetMode(Mode mode);
 
   DISALLOW_COPY_AND_ASSIGN(MaterialDesignController);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MATERIAL_DESIGN_MATERIAL_DESIGN_CONTROLLER_H_