Remove ability to switch to pre-MD UI from about:flags.

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"
 
 namespace ui {
 
 namespace test {
 class MaterialDesignControllerTestAPI;
 }  // namespace test
 
 // Central controller to handle material design modes.
 class UI_BASE_EXPORT MaterialDesignController {
  public:
   // The different material design modes. The order cannot be changed without
   // updating references as these are used as array indices.
   enum Mode {
-    // Classic, non-material design.
-    NON_MATERIAL = 0,
     // Basic material design.
     MATERIAL_NORMAL = 1,
     // Material design targeted at mouse/touch hybrid devices.
     MATERIAL_HYBRID = 2
   };
 
   // Initializes |mode_|. Must be called before checking |mode_|.
   static void Initialize();
 
   // 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.
+  // Returns true. TODO(estade): remove.
   static bool IsModeMaterial();
 
   // Returns true if the current mode is a material design variant and this mode
   // should be extended to cover secondary UI.
   static bool IsSecondaryUiMaterial();
 
   // Returns the per-platform default material design variant.
   static Mode DefaultMode();
 
   static bool is_mode_initialized() { return is_mode_initialized_; }
@@ skipping 24 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_