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

ui/views/views_delegate.h

Index: ui/views/views_delegate.h
diff --git a/ui/views/views_delegate.h b/ui/views/views_delegate.h
index 5ab30aa42997cf7bb298dcdf71caab5b07eb9c29..61f7c850113b3c42ce6ffca92b65bb57911e922b 100644
--- a/ui/views/views_delegate.h
+++ b/ui/views/views_delegate.h
@@ -71,6 +71,9 @@ enum class InsetsMetric {
   DIALOG_BUTTON,
   // The insets that should be applied around a dialog's frame view.
   DIALOG_FRAME_VIEW,
+  // Padding to add to vector image buttons to increase their click and touch
+  // target size.
+  VECTOR_IMAGE_BUTTON_PADDING,
 };
 
 enum class DistanceMetric {