Use an InsetMetric instead of a constant for vector button padding.

ui/views/controls/button/image_button_factory.cc

 // Copyright 2017 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 "ui/views/controls/button/image_button_factory.h"
 
 #include "ui/gfx/color_utils.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/gfx/vector_icon_types.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/button/custom_button.h"
 #include "ui/views/controls/button/image_button.h"
 #include "ui/views/painter.h"
+#include "ui/views/views_delegate.h"
 
 namespace views {
 
 ImageButton* CreateVectorImageButton(ButtonListener* listener) {
   ImageButton* button = new ImageButton(listener);
   button->SetInkDropMode(CustomButton::InkDropMode::ON);
   button->set_has_ink_drop_action_on_click(true);
   button->SetImageAlignment(ImageButton::ALIGN_CENTER,
                             ImageButton::ALIGN_MIDDLE);
   button->SetFocusPainter(nullptr);
-  // Extra space around the buttons to increase their event target size.
-  constexpr int kButtonExtraTouchSize = 4;
-  button->SetBorder(CreateEmptyBorder(gfx::Insets(kButtonExtraTouchSize)));
+  button->SetBorder(
+      CreateEmptyBorder(ViewsDelegate::GetInstance()->GetInsetsMetric(
+          InsetsMetric::VECTOR_IMAGE_BUTTON_PADDING)));
   return button;
 }
 
 void SetImageFromVectorIcon(ImageButton* button,
                             const gfx::VectorIcon& icon,
                             SkColor related_text_color) {
   const SkColor icon_color =
       color_utils::DeriveDefaultIconColor(related_text_color);
   const SkColor disabled_color = SkColorSetA(icon_color, 0xff / 2);
   button->SetImage(CustomButton::STATE_NORMAL,
                    gfx::CreateVectorIcon(icon, icon_color));
   button->SetImage(CustomButton::STATE_DISABLED,
                    gfx::CreateVectorIcon(icon, disabled_color));
   button->set_ink_drop_base_color(icon_color);
 }
 
 }  // views