Make MdTextButton a LabelButton, use it in the DL shelf.

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 "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
@@ skipping 27 matching lines @@
   LabelButton(ButtonListener* listener, const base::string16& text);
   ~LabelButton() override;
 
   // Gets or sets the image shown for the specified button state.
   // GetImage returns the image for STATE_NORMAL if the state's image is empty.
   virtual const gfx::ImageSkia& GetImage(ButtonState for_state);
   void SetImage(ButtonState for_state, const gfx::ImageSkia& image);
 
   // Gets or sets the text shown on the button.
   const base::string16& GetText() const;
-  void SetText(const base::string16& text);
+  virtual void SetText(const base::string16& text);
 
   // Sets the text color shown for the specified button |for_state| to |color|.
   void SetTextColor(ButtonState for_state, SkColor color);
 
   // Sets the text colors shown for the non-disabled states to |color|.
   void SetEnabledTextColors(SkColor color);
 
   // Sets drop shadows underneath the text.
   void SetTextShadows(const gfx::ShadowValues& shadows);
 
@@ skipping 81 matching lines @@
   gfx::Rect GetThemePaintRect() const override;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, Init);
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, Label);
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, Image);
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, LabelAndImage);
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, FontList);
   FRIEND_TEST_ALL_PREFIXES(LabelButtonTest, ButtonStyleIsDefaultSize);
 
+  void SetTextInternal(const base::string16& text);
+
   // View:
   void ChildPreferredSizeChanged(View* child) override;
 
   // NativeThemeDelegate:
   ui::NativeTheme::Part GetThemePart() const override;
   ui::NativeTheme::State GetThemeState(
       ui::NativeTheme::ExtraParams* params) const override;
   const gfx::Animation* GetThemeAnimation() const override;
   ui::NativeTheme::State GetBackgroundThemeState(
       ui::NativeTheme::ExtraParams* params) const override;
@@ skipping 54 matching lines @@
   gfx::HorizontalAlignment horizontal_alignment_;
 
   scoped_ptr<Painter> focus_painter_;
 
   DISALLOW_COPY_AND_ASSIGN(LabelButton);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_BUTTON_LABEL_BUTTON_H_