Make the extra padding around VectorIconButtons configurable.

chrome/browser/ui/views/harmony/layout_delegate.h

Index: chrome/browser/ui/views/harmony/layout_delegate.h
diff --git a/chrome/browser/ui/views/harmony/layout_delegate.h b/chrome/browser/ui/views/harmony/layout_delegate.h
index 737d56e896a0c01a445c86ff1814472679d7db83..25eaf0f98bc418ec440726b7e2c72181a0362e34 100644
--- a/chrome/browser/ui/views/harmony/layout_delegate.h
+++ b/chrome/browser/ui/views/harmony/layout_delegate.h
@@ -10,6 +10,11 @@
 class LayoutDelegate {
  public:
   enum class Metric {
+    // Extra padding added on all sides of a button's content.  This is only
+    // used for certain button types.
+    // TODO(pkasting): This should probably be touch-specific and needs to be
+    // considered more holistically.
+    BUTTON_PADDING,
     // Horizontal or vertical margin between the edge of a dialog and a
     // contained button.
     DIALOG_BUTTON_MARGIN,