[MD] simplify and unify some ink drop center calculations

chrome/browser/ui/views/toolbar/back_button.h

 // 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.
 
 #ifndef CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_
 #define CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_
 
 #include "base/macros.h"
 #include "chrome/browser/ui/views/toolbar/toolbar_button.h"
 
@@ skipping 21 matching lines @@
 
   // Sets |margin_leading_| when the browser is maximized and updates layout
   // to make the focus rectangle centered.
   void SetLeadingMargin(int margin);
 
  private:
   // ToolbarButton:
   const char* GetClassName() const override;
   scoped_ptr<views::LabelButtonBorder> CreateDefaultBorder() const override;
   gfx::Rect GetThemePaintRect() const override;
-  gfx::Point GetInkDropCenter() const override;
 
   // Any leading margin to be applied. Used when the back button is in
   // a maximized state to extend to the full window width.
   int margin_leading_;
 
   DISALLOW_COPY_AND_ASSIGN(BackButton);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_TOOLBAR_BACK_BUTTON_H_