[MD] simplify and unify some ink drop center calculations

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

 // 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.
 
 #include "chrome/browser/ui/views/toolbar/back_button.h"
 
 #include "ui/gfx/geometry/insets.h"
 #include "ui/views/animation/ink_drop_animation_controller.h"
 #include "ui/views/controls/button/label_button_border.h"
 #include "ui/views/painter.h"
@@ skipping 11 matching lines @@
   UpdateThemedBorder();
 
   const int inset = LabelButton::kFocusRectInset;
   const bool is_rtl = base::i18n::IsRTL();
   const gfx::Insets insets(inset, inset + (is_rtl ? 0 : margin),
                            inset, inset + (is_rtl ? margin : 0));
   SetFocusPainter(views::Painter::CreateDashedFocusPainterWithInsets(insets));
   InvalidateLayout();
 }
 
-gfx::Point BackButton::GetInkDropCenter() const {
-  int visible_width = GetPreferredSize().width();
-  return gfx::Point(
-      GetMirroredXWithWidthInView(margin_leading_, visible_width) +
-          visible_width / 2,
-      height() / 2);
-}
-
 const char* BackButton::GetClassName() const {
   return "BackButton";
 }
 
 scoped_ptr<views::LabelButtonBorder> BackButton::CreateDefaultBorder() const {
   scoped_ptr<views::LabelButtonBorder> border =
       ToolbarButton::CreateDefaultBorder();
 
   // Adjust border insets to follow the margin change,
   // which will be reflected in where the border is painted
   // through GetThemePaintRect().
   const gfx::Insets insets(border->GetInsets());
   border->set_insets(gfx::Insets(insets.top(), insets.left() + margin_leading_,
                                  insets.bottom(), insets.right()));
 
   return border;
 }
 
 gfx::Rect BackButton::GetThemePaintRect() const {
   gfx::Rect rect(LabelButton::GetThemePaintRect());
   const bool is_rtl = base::i18n::IsRTL();
   rect.Inset(is_rtl ? 0 : margin_leading_, 0, is_rtl ? margin_leading_ : 0, 0);
   return rect;
 }