Make the extra padding around VectorIconButtons configurable.

ui/views/layout/layout_constants.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_LAYOUT_LAYOUT_CONSTANTS_H_
 #define UI_VIEWS_LAYOUT_LAYOUT_CONSTANTS_H_
 
 #include "build/build_config.h"
 #include "ui/views/layout/grid_layout.h"
 
@@ skipping 58 matching lines @@
 // Horizontal spacing between the edge of the window and the
 // left or right of a button (when using new style dialogs).
 constexpr int kButtonHEdgeMarginNew = 20;
 
 // Spacing between the edge of the window and the edge of the close button.
 const int kCloseButtonMargin = 7;
 
 // Horizontal spacing between buttons that are logically related.
 constexpr int kRelatedButtonHSpacing = 6;
 
+// Extra space around the buttons to increase their event target size.
+const int kButtonExtraTouchSize = 4;
+
 // Indent of checkboxes relative to related text.
 constexpr int kCheckboxIndent = 10;
 
 // Horizontal spacing between the end of an item (i.e. an icon or a checkbox)
 // and the start of its corresponding text.
 constexpr int kItemLabelSpacing = 10;
 
 // Padding on the left and right of a button's contents.
 const int kButtonHorizontalPadding = 16;
 
 // Default minimum width of buttons.
 const int kMinimumButtonWidth = 48;
 
 // Minimum width of dialog buttons.
 const int kDialogMinimumButtonWidth = 75;
 
 }  // namespace views
 
 #endif  // UI_VIEWS_LAYOUT_LAYOUT_CONSTANTS_H_