Make the extra padding around VectorIconButtons configurable.

ui/views/views_delegate.cc

Index: ui/views/views_delegate.cc
diff --git a/ui/views/views_delegate.cc b/ui/views/views_delegate.cc
index 8a78a96dedebbfa88229cb5d34284fd31393e216..1a82e6ccb3d14ae201dd7a2ae6bbe8bafd882ebd 100644
--- a/ui/views/views_delegate.cc
+++ b/ui/views/views_delegate.cc
@@ -164,6 +164,10 @@ int ViewsDelegate::GetButtonHorizontalPadding() const {
   return kButtonHorizontalPadding;
 }
 
+gfx::Insets ViewsDelegate::GetButtonMargins() const {
+  return gfx::Insets(kButtonExtraTouchSize);
+}
+
 ViewsDelegate::ViewsDelegate()
     : views_tsc_factory_(new ViewsTouchEditingControllerFactory) {
   DCHECK(!views_delegate);