Introduce new flag to control usage of MD in secondary (not top-chrome)

ui/views/controls/button/label_button.h

 // Copyright (c) 2012 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_VIEWS_CONTROLS_BUTTON_LABEL_BUTTON_H_
 #define UI_VIEWS_CONTROLS_BUTTON_LABEL_BUTTON_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
@@ skipping 113 matching lines @@
 
   // CustomButton:
   void StateChanged() override;
 
   // Fills |params| with information about the button.
   virtual void GetExtraParams(ui::NativeTheme::ExtraParams* params) const;
 
   // Resets colors from the NativeTheme, explicitly set colors are unchanged.
   virtual void ResetColorsFromNativeTheme();
 
+  // Changes the visual styling of this button to reflect the state of
+  // |is_default()|.
+  virtual void UpdateStyleToIndicateDefaultStatus();
+
   // Updates the image view to contain the appropriate button state image.
   void UpdateImage();
 
   // Updates the border as per the NativeTheme, unless a different border was
   // set with SetBorder.
   void UpdateThemedBorder();
 
   // NativeThemeDelegate:
   gfx::Rect GetThemePaintRect() const override;
 
@@ skipping 78 matching lines @@
   gfx::HorizontalAlignment horizontal_alignment_;
 
   std::unique_ptr<Painter> focus_painter_;
 
   DISALLOW_COPY_AND_ASSIGN(LabelButton);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_LABEL_BUTTON_H_